SQuInT 2022 Program
Full Program | Thursday | Friday | Saturday | All Sessions | Posters | Talks
SESSION 1: Neutral atoms (Islands Ballroom)Chair: (Jonathan King (Atom Computing)) | |
| 8:30 am - 9:15 am | Adam Kaufman, UC Boulder (invited) Quantum science with microscopically-controlled arrays of alkaline-earth atoms | Abstract. Quantum science with neutral atoms has seen great advances in the past two decades. Many of these advances follow from the development of new techniques for cooling, trapping, and controlling atomic samples. In this talk, I will describe ongoing work where we have explored a new type of atom - alkaline-earth(-like) atoms - for optical tweezer trapping, a technology which allows microscopic control of arrays of 100s to potentially 1000s of atoms. While their increased complexity leads to challenges, alkaline-earth atoms offer new scientific opportunities by virtue of their rich internal degrees of freedom. Combining features of these atoms with tweezer-based control has impacted multiple areas in quantum science, including quantum information processing, quantum simulation, and quantum metrology. |
| 9:15 am - 9:45 am | Yue-Hui Lu, University of California Berkeley Cavity Detection with Single Atom Array | Abstract. We place single atoms inside of high-finesse optical cavity using optical tweezer array. This allows us to: 1. Characterize the dichromatic cavity modes profile using fluorescent single atoms as scanning probes. We demonstrate beyond diffraction limit resolution microscopy of the cavity mode axial and radial patterns. 2.Sequentially state measurement of single atoms with high fidelity and fast speed while maintaining the state coherence of the rest of the atom array. We present this as a means of mid-quantum-circuit measurement protocol, an essential building block for atom array quantum computing. 3.Position multiple atoms inside the cavity mode in spatial patterns that exhibit super/sub-radiance under side pumping, and much more. |
| 9:45 am - 10:15 am | Pablo Poggi, University of New Mexico Period-multiplexing Floquet Time Crystals in spin systems with multi-body interactions | Abstract. We show the emergence of Floquet time crystal (FTC) phases in periodically driven p-spin models, which describe a collection of spin-1/2 particles with all-to-all p-body interactions. Given the mean-field nature of these models, we treat the problem exactly in the thermodynamic limit and show that, for a given value of p, these systems can host various robust time-crystalline responses with period nT,whereT is the period of the drive and n an integer between 2 and p. In particular, the case of four-body interactions (p = 4) gives rise to both a usual period-doubling crystal and also a novel period-quadrupling phase. On the theoretical front, we develop a comprehensive framework to predict robust subharmonic response in classical area-preserving maps, and use this as a basis to predict the occurrence and characterize the stability of the resulting mean-field FTC phases in the quantum regime. Then, we experimentally study these models using a small quantum processor based on atomic spins, and examine the various challenges associated with identifying FTC phases from experimental data. Finally, we discuss applications of Floquet Time Crystals in quantum technologies. |
SESSION 2: Quantum sensing (Islands Ballroom)Chair: (Todd Brun (University Southern California)) | |
| 10:45 am - 11:30 am | Quntao Zhuang, University of Southern California (invited) Quantum metrology for dark matter search | Abstract. Quantum metrology is able to boost measurement precision in various applications. In this talk, I will use dark matter search as an example, to explain some ways how quantum sensing works and what advantages it can provide. I will start with an ultimate bound for noise sensing and its implication in dark matter search with microwave cavities - the ultimate limit of the 'scan-rate' given arbitrary input source and detection. Then I will talk about optimal schemes based on two-mode squeezing and a 'nulling' receiver. Afterwards, I will extend to an entangled sensor array (as axion wave length is huge), showing the boost of the scaling of scan-rate from coherent-signal processing and the joint noise suppression from multi-partite entanglement. Finally, I will discuss about generalization to opto-mechanical sensor arrays - for the detection of another hypothesis of dark matter called B-L model. |
| 11:30 am - 12:00 pm | Kianna Wan, Stanford University New bounds on adaptive quantum metrology under Markovian noise | Abstract. We analyse the problem of estimating a scalar parameter g that controls the Hamiltonian of a quantum system subject to Markovian noise. Specifically, we place bounds on the growth rate of the quantum Fisher information with respect to g, in terms of the Lindblad operators and the g-derivative of the Hamiltonian H. Our new bounds are not only more generally applicable than those in the literature---for example, they apply to systems with time-dependent Hamiltonians and/or Lindblad operators, and to infinite-dimensional systems such as oscillators---but are also tighter in the settings where previous bounds do apply. We derive our bounds directly from the master equation describing the system, without needing to discretize its time evolution. We also use our results to investigate how sensitive a single detection system can be to signals with different time dependences. We demonstrate that the sensitivity bandwidth is related to the quantum fluctuations of dH/dg, illustrating how "non-classical" states can enhance the range of signals that a system is sensitive to, even when they cannot increase its peak sensitivity. |
SESSION 3: Computer science perspective (Islands Ballroom)Chair: (Milad Marvian (UNM)) | |
| 1:30 pm - 2:15 pm | Ewin Tang, University of Washington (invited) Query-optimal estimation of unitary channels in diamond distance | Abstract. We will present an algorithm to learn an unknown unitary channel acting on a d-dimensional qudit to diamond-norm error \(\varepsilon\), using \(O(d^2/\varepsilon)\) applications of the unknown channel and only one qudit. This algorithm uses the optimal number of qudits and number of queries up to a sub-logarithmic factor, even if one has access to the inverse or controlled versions of the unknown unitary. This improves over prior work, which achieves entanglement infidelity \(\delta\) using \(O(d^2/\sqrt{\delta})\) applications in parallel, thereby requiring \(\Omega(d^2)\) qudits. Based on joint work with Jeongwan Haah, Robin Kothari, and Ryan O'Donnell. |
| 2:15 pm - 2:45 pm | Austin Daniel, University of New Mexico CQuIC Adaptive measurement-based quantum computation of classical Boolean functions: Exponential reductions in space-time resources | Abstract. We study the resource costs required to compute a variety of nonlinear Boolean functions via adaptive measurement-based quantum computation (MBQC) with a mod-2 linear classical side-processor, better known as \(l2\)-MBQC. We give an explict example of how constant-depth quantum circuits with the aid of mid-circuit measurements can compute the so-called mod-3 function on \(n\)-bits---and more generally mod-\(p\) functions for any prime \(p\)---using an \(O(n)\) qubit resource state and a constant number of rounds of interaction with the classical side-processor. In constrast, we show that the same task requires \(\Omega(2^n)\) qubits in the nonadaptive setting. Our results also give an oracular separation between the power of constant-depth quantum circuits and constant-depth classical circuits with unbounded fan-in NAND and mod-\(p\) gates. |
SESSION 4: Quantum algorithms (Islands Ballroom)Chair: (Nathan Wiebe (Toronto)) | |
| 3:15 pm - 3:45 pm | Joonho Lee, Google A path forward for achieving practical quantum advantage in chemistry | Abstract. In this talk, I will describe a new hybrid algorithm, quantum-classical hybrid quantum Monte Carlo (QC-QMC), that has demonstrated accurate quantum computations of chemical systems beyond what has been possible with other variational NISQ algorithms. I will explain what algorithms need to consider when showing practical quantum advantages and why QC-QMC has attractive features. I will also remark on challenges in QC-QMC that must be considered when designing one of the first demonstrations for quantum advantage in chemistry. This talk is meant to engage both chemistry and quantum information science audiences as the synergistic interactions between the two are critical. |
| 3:45 pm - 4:15 pm | Anirban Chowdhury, Institute for Quantum Computing Classical and quantum algorithms for trace estimation | Abstract. Estimating the trace of matrix functions is a problem commonly encountered in physics. In this talk I will present improved exponential-time classical and quantum algorithms for the problem of trace estimation, with the partition function as a specific example. I will summarize techniques to evaluate traces of block-encoded operators on quantum devices. I will show that a compression technique based on unitary 2-designs leads to a qubit-efficient quantum algorithm for estimating partition functions. I will then discuss how the same compression idea also leads to a classical algorithm with improved running-time. Lastly, I will mention some complexity theoretic results regarding the hardness of this problem. The talk will be based on some results from arXiv:2110.15466. |
| 4:15 pm - 4:45 pm | Burak Sahinoglu, PsiQuantum Quantum algorithms from fluctuation theorems: Thermal-state preparation | Abstract. Fluctuation theorems provide a correspondence between properties of quantum systems in thermal equilibrium and a work distribution arising in a non-equilibrium process that connects two quantum systems with Hamiltonians \(H_0\) and \(H_1=H_0+V\). Building upon these theorems, we present a quantum algorithm to prepare a purification of the thermal state of \(H_1\) at inverse temperature \(\beta \ge 0\) starting from a purification of the thermal state of \(H_0\). The complexity of the quantum algorithm, given by the number of uses of certain unitaries, is \(\tilde {\cal O}(e^{\beta (\Delta \! A- w_l)/2})\), where \(\Delta \! A\) is the free-energy difference between \(H_1\) and \(H_0,\) and \(w_l\) is a work cutoff that depends on the properties of the work distribution and the approximation error \(\epsilon>0\). If the non-equilibrium process is trivial, this complexity is exponential in \(\beta \|V\|\), where \(\|V\|\) is the spectral norm of \(V\). This represents a significant improvement of prior quantum algorithms that have complexity exponential in \(\beta \|H_1\|\) in the regime where \(\|V\|\ll \|H_1\|\). The dependence of the complexity in \(\epsilon\) varies according to the structure of the quantum systems. It can be exponential in \(1/\epsilon\) in general, but we show it to be sublinear in \(1/\epsilon\) if \(H_0\) and \(H_1\) commute, or polynomial in \(1/\epsilon\) if \(H_0\) and \(H_1\) are local spin systems. The possibility of applying a unitary that drives the system out of equilibrium allows one to increase the value of \(w_l\) and improve the complexity even further. To this end, we analyze the complexity for preparing the thermal state of the transverse field Ising model using different non-equilibrium unitary processes and see significant complexity improvements. |
SESSION 5: Poster Session (Sierra Nevada Foyer) | |
SESSION 6: Quantum optics and network (Islands Ballroom)Chair: (Elohim Becerra (UNM)) | |
| 8:30 am - 9:15 am | Joseph Lukens, Oak Ridge National Lab (invited) Elastic optical quantum networks: connecting two worlds | Abstract. Lightwave technology has revolutionized networking, enabling a vast global infrastructure of high-speed communications that supports the internet today. Throughout this development, elastic or flex-grid optical networking has proven itself a powerful paradigm for maximizing utilization of optical resources via reconfigurable allocation of wavelength channels and bandwidths matched to user demand. In this talk, I will describe research expanding elastic optical networking to quantum networks as well. Through routing and provisioning of broadband photonic entanglement with wavelength-selective switches, quantum networks of ever-increasing size can be envisioned, as indicated by our proof-of-principle experiments demonstrating adaptive polarization entanglement distribution in a deployed quantum local area network. After discussing the integration of important practical capabilities into our testbed - including White Rabbit timing synchronization and quantum key distribution - I will conclude with recent efforts toward scaling to much larger networks, focusing on addressable ultrabroadband entanglement sources, genetic-algorithm-aided design, and Bayesian inference. As a bridge connecting highly successful classical optical networks to their more nascent quantum counterparts, elastic optical networking should continue to offer a valuable framework in which quantum networks can thrive and grow in both size and functionality. |
| 9:15 am - 9:45 am | Matthew Brown, University of Oregon Quantum advantage in interferometric imaging | Abstract. Just over 100 years ago, Michelson and Pease measured the diameter of a star using the interference of visible-spectrum light fields collected at two positions in an apertured telescope. The spatial coherence, distilled from a spatially incoherent object through propagation, between the collected light fields is guaranteed by the van Cittert-Zernike theorem. The angular resolution of the collection of apertures is limited by the separation of apertures, rather than the size of a single aperture. This technique has been employed recently in radio astronomy to image supermassive black holes. Yet, measurements in the visible spectrum are limited to comparatively short baselines due to loss or cost, whereas the radio regime circumvents this issue by measuring the electric field at each location. In 2012, Gottesman, Jennewein and Croke suggested using a nonlocally distributed single photon as a phase reference, increasing the telescope separation using quantum repeaters to overcome loss. In a first of a kind measurement, we report the use of a heralded single photon from a pulsed, parametric downconversion source as a non-local oscillator to image a double-slit intensity pattern illuminating a diffuser that has a matching single temporal-spectral mode, Lambertian scattering, and approximate spatial incoherence. Using signal-to-noise ratio per coincidence as a metric, we find that the nonlocal oscillator outperforms a weak classical local oscillator. |
| 9:45 am - 10:15 am | Prajit Dhara, University of Arizona Zero-Added-Loss Entangled Photon Multiplexing for Ground- and Space-Based Quantum Networks | Abstract. We propose a scheme for optical entanglement distribution in quantum networks based on a quasi-deterministic entangled photon pair source. By combining heralded photonic Bell pair generation with spectral mode conversion to interface with quantum memories, the scheme eliminates switching losses due to multiplexing. We analyze this 'zero-added-loss multiplexing' (ZALM) Bell pair source for the particularly challenging problem of long-baseline entanglement distribution via satellites and ground-based memories, where it unlocks additional advantages: (i) the substantially higher channel efficiency \(\eta\) of downlinks vs. uplinks with realistic adaptive optics, and (ii) photon loss occurring before interaction with the quantum memory - i.e., Alice and Bob receiving rather than transmitting - improve entanglement generation rate scaling by \(O\sqrt \eta\). Based on numerical analyses, we estimate our protocol to achieve \(>10^2 ebits/s\) at memory multiplexing of \(10^4\) spin qubits for ground distance larger than \(10^4\) km, with the spin-spin Bell state fidelity exceeding 99%. Our architecture presents a blueprint for realizing global-scale quantum networks in the near term. Additionally, we demonstrate the utility of the proposed architecture for ground quantum networks when deployed on a linear quantum repeater chain. |
SESSION 7: NISQ toolbox (Islands Ballroom)Chair: (Joshua Combes (CU Boulder)) | |
| 10:45 am - 11:30 am | Victor Albert , NIST (invited) Modern quantum tools for bosonic systems | Abstract. I overview ongoing efforts to extend state-of-the-art discrete-variable (DV) tomographic, error-correction, and cryptographic protocols to bosonic systems, including: (1) a theory of appropriately defined CV state designs, and their applications to design-based CV shadow tomography; (2) a cryptographic protocol utilizing squeezed states whose proof of security is based on a CV extension of DV monogamy-of-entanglement games; (3) sample efficiency of homodyne and photon-number-resolving tomography obtained via recasting said protocols in terms of shadow tomography; and (4) a unified decoding framework for concatenated DV and CV error-correcting codes. |
| 11:30am-12:00pm | Thomas O'Brien, Google Error mitigation of correlated electronic structure simulations on a quantum device | Abstract. One of the main markers of progress in the development of useful quantum computing devices is the simulation of ever more challenging physical systems. As the complexity of the physical system grows the importance of robust and scalable error mitigation strategies increases as well --- especially for near term quantum devices. Herein we push towards the full complexity demanded for real-world electronic structure simulations on quantum hardware, by simulating ground states of systems projected into a pairing subspace known as seniority zero. Studying physical simulation within the seniority zero approximation affords a computational stepping stone to a fully correlated model to validate the scalablity of recent error mitigation strategies. We examine the performance of combined variational relaxation, accounting for coherent quantum device errors, and error mitigation based on doubling quantum resources in time (echo verification). We prepare ground states of correlated electronic systems on 10-qubit systems to a typical relative accuracy of 0.45%, and achieve an up to 300-fold reduction of error over simple post-selection. Our results frame the potential of near-term quantum processors to provide computational advantages for correlated electronic structure problems. |
SESSION 8: Ion-trap quantum computing (Islands Ballroom)Chair: (Sara Mouradian (Washington)) | |
| 1:30 pm - 2:15 pm | Crystal Noel, Duke (invited) Efficient tests of quantumness implemented on a trapped-ion quantum computer | Abstract. A test of quantumness is a protocol where a classical user issues challenges to a quantum device to determine if it exhibits non-classical behavior, under certain cryptographic assumptions. Interactive challenges can be used for tests of quantumness. They require only classical communication and are efficiently verifiable. In this talk, I will show how we implement the first interactive protocol using a trapped ion quantum computer. I will also describe how we execute an efficient non-interactive test of quantumness by modifying the original protocol. Our results significantly exceed the bound for a classical device's success. |
| 2:15 pm - 2:45 pm | Omid Khosravani, Duke University Noise-resilient quantum control | Abstract. One of the main obstacles in scaling up quantum computers is the accumulated noise throughout the quantum circuit. Various error-mitigation and quantum error-correction techniques have been proposed to mitigate and correct the noise. However, these techniques often come with substantially resource requirements that are highly sensitive to the infidelity of quantum gates. However, quantum gates are afflicted by various sources of coherent and incoherent noise that are embedded in quantum control as well as the qubit imperfections and the qubit environment which limits quantum gate fidelities. Here we present a theoretical framework as well as experimental demonstration for quantum gates that are insensitive to well-defined sources of noise up to a specified order. We first show how the quantum control problem can be cast into an optimization problem and provide a path integral picture to justify the noise-resilience of our quantum control framework. We then demonstrate our protocol by generating frequency-amplitude-phase modulated pulses to obtain high-fidelity two-qubit gates in a chain of trapped-ions. We model various sources of noise in two-qubit gates with trapped-ions including correlated electric fields, trap potential irregularities, crosstalk, as well as fluctuations in laser amplitude, frequency and phase, and show how they are mitigated within our framework. We finally discuss how our framework can be readily applied to two-qubit gates with superconducting qubits. |
| 2:45 pm - 3:15 pm | Nicole Greene, University of California Berkeley Demonstration of near-infrared light shift gate on optical qubits and investigation of laser noise impact on gate fidelity | Abstract. The typical native entangling gate for trapped ion systems is the Mølmer Sørensen gate. Here we demonstrate a wavelength insensitive alternative, the light shift gate, on a pair of Ca 40 ions. Instead of driving red and blue tones, we construct a running lattice to impart a time varying state dependent force on the ion pair. This gate has many advantages such as a better interaction strength scaling with power (linear with power instead of electric field), wavelength insensitivity allowing us to work with IR light, which is more ideal for integrated optics applications, and because it is a σz⊗σz interaction, spin echo pulses commute with the gate eliminating σz errors from unwanted stark shifts or drifts in laser frequency. We are working with an optical qubit (729nm transition) and using 794nm light to drive the gate. Because we are driving the gate near a dipole transition and we specifically accumulate phase on the D state making for simpler gate dynamics. We study how it performs under various parameters such as speed, ion spacing, and motional heating. Additionally, we investigate how laser noise reduces fidelity. We attempt to quantify what range constitute "medium" noise which is too slow to be averaged out, but too fast relative to the gate time to act as a constant offset. |
SESSION 9a: Learning with NISQ devices (Islands Ballroom I)Chair: (Philip Blocher (UNM)) | |
| 3:45 pm - 4:15 pm | Haimeng Zhang, University of Southern California Predicting non-Markovian superconducting qubit dynamics from tomographic reconstruction | Abstract. Non-Markovian noise presents a particularly relevant challenge in understanding and combating decoherence in quantum computers, yet is challenging to capture in terms of simple models. Here we show that a simple phenomenological dynamical model known as the post-Markovian master equation (PMME) accurately captures and predicts non-Markovian noise in a superconducting qubit system. The PMME is constructed using experimentally measured state dynamics of an IBM Quantum Experience cloud-based quantum processor, and the model thus constructed successfully predicts the non-Markovian dynamics observed in later experiments. The model also allows the extraction of information about crosstalk and measures of non-Markovianity. We demonstrate definitively that the PMME model predicts subsequent dynamics of the processor better than the standard Markovian master equation. |
| 4:15 pm - 4:45 pm | Max D. Porter, Laurence Livermore National Laboratory Impact of dynamics, entanglement, and incoherent noise on the fidelity of few-qubit digital quantum simulation | Abstract. Quantum chaotic simulations stand to be one of the most important application areas for quantum computing. This is due to the need to simulate these systems numerically and the exponential resources needed to simulate them on classical computers. We study the quantum sawtooth map (QSM), a gate- and qubit-efficient system, as a prototypical example of quantum chaotic Hamiltonian simulation. We investigate the interaction of a gate-based Lindblad noise model with localization and diffusion in the QSM. Theoretical expressions for the fidelity decays of each are derived, validated with simulation, and their difference qualitatively observed in experiment. We find the rate of fidelity decay increases continuously from fully localized to fully diffusive dynamics due to both increased dephasing and a partial relaxation caused by random entanglement. From experiment the “effective” T1 and T2 times are extracted by fitting theory and simulations to data from IBM-Q. The effective T2 time is found to be 2.7x worse than reported for single-qubit T2, and the CNOT gate error is up to 4.5x worse than reported for randomized benchmarking. This illustrates the importance of complex dynamics for benchmarking near-term quantum devices. *Work for LLNL-ABS-838050 was prepared for US DOE by LLNL under Contract DE-AC52-07NA27344 and was supported by the DOE Office of Fusion Energy Sciences “Quantum Leap for Fusion Energy Sciences” project AT1030200-SCW1680. |
| 4:45 pm - 5:15 pm | Elijah Pelofske, Los Alamos National Laboratory Quantum Volume in Practice: What Users Can Expect from NISQ Devices | Abstract. Quantum volume (QV) has become the de-facto standard benchmark to quantify the capability of Noisy Intermediate-Scale Quantum (NISQ) devices. While QV values are often reported by NISQ providers for their systems, we perform our own series of QV calculations on 24 NISQ devices currently offered by IBM~Q, IonQ, Rigetti, Oxford Quantum Circuits, and Quantinuum (formerly Honeywell). Our approach characterizes the performances that an advanced user of these NISQ devices can expect to achieve with a reasonable amount of optimization, but without white-box access to the device. In particular, we compile QV circuits to standard gate sets of the vendor using compiler optimization routines where available, and we perform experiments across different qubit subsets. We find that running QV tests requires very significant compilation cycles, QV values achieved in our tests typically lag behind officially reported results and also depend significantly on the classical compilation effort invested. |
| 5:15 pm - 5:45 pm | Akshay Seshadri, University of Colorado Versatile fidelity estimation with confidence | Abstract. As quantum devices become more complex and the requirements on these devices become more demanding, it is crucial to be able to verify the performance of such devices in a scalable and reliable fashion. A cornerstone task in this challenge is quantifying how close an experimentally prepared quantum state is to the desired one. Here we present a method to construct an estimator for the quantum state fidelity that is compatible with any measurement protocol. Our method provides a confidence interval on this estimator that is guaranteed to be nearly minimax optimal for the specified measurement protocol. For a well-chosen measurement scheme, our method is competitive in the number of measurement outcomes required for estimation. We demonstrate our method using simulations and experimental data from a trapped-ion quantum computer, and compare the results with other methods. Through a combination of theoretical and numerical results, we show various desirable properties for our method: robustness against experimental imperfections, competitive sample complexity, and accurate estimates in practice. Our method can be easily extended to estimate the expectation value of any observable, such as entanglement witnesses. |
| 5:45 pm - 6:15 pm | Shamminuj Aktar, New Mexico State University State Preparation Fidelities for Dicke States | Abstract. Estimating the fidelity of highly entangled states on NISQ devices is an important benchmarking task. We present a divide-and-conquer approach to deterministically prepare Dicke states (equal-weight superpositions of all n-qubit states with Hamming Weight k) and measure their experimental state preparation fidelity on superconducting devices with LNN and ion-trap devices with all-to-all connectivity: (i) We design linear-depth Dicke state preparation circuits which first divide the Hamming weight between blocks of n/2 qubits, and then conquer those blocks with improved versions of Dicke state unitaries [arXiv:1904.07358], including versions for both LNN and all-to-all connectivity. (ii) Experimental evaluation up to n=6 on IBMQ Sydney and Montreal devices using 3^n state tomography settings gives significantly higher state fidelity compared to previous results [arXiv:2007.01681,1807.05572], due to more efficient circuits, measurement error mitigation, and hardware improvement. (iii) Further, we use techniques to give lower bounds for state preparation fidelities using only 3 measurement settings [arXiv:quant-ph/0606023]. These bounds have so far not been tight enough to provide reasonable estimations for larger states on NISQ devices, including (ii). 15 years after the technique's introduction, we report meaningful lower bounds for the state preparation fidelity of all Dicke States up to n=10 on the Quantinuum H1 system. (ii): arXiv:2112.12435 (iii): work in progress |
SESSION 9b: Algorithms in NISQ era (Islands Ballroom II)Chair: (Jun Takahashi (UNM)) | |
| 3:45 pm - 4:15 pm | Frederic Sauvage, Los Alamos National Laboratory Building spatial symmetries into parameterized quantum circuits for faster training | Abstract. Practical success of quantum learning models hinges on having a suitable structure for the parameterized quantum circuit employed . Such structure is defined both by the types of gates employed and by the correlations of their parameters. While much research has been devoted to devising adequate gate-sets, typically respecting some symmetries of the problem, very little is known about how their parameters should be structured. In this work, we show that an ideal parameter structure naturally emerges when carefully considering spatial symmetries (i.e., the symmetries that are permutations of parts of the system under study). Namely, we consider the automorphism group of the problem Hamiltonian, leading us to develop a circuit construction that is equivariant under this symmetry group. The benefits of our novel circuit structure, called ORB, are numerically probed in several ground-state problems. We find a consistent improvement (in terms of circuit depth, number of parameters required, and gradient magnitudes) compared to literature circuit constructions. |
| 4:15 pm - 4:45 pm | Nic Ezzell, University of Southern California Quantum mixed state compiling and the quantum low-rank approximation problem | Abstract. We present a variational quantum algorithm (VQA) to compile mixed states which is suitable for near-term hardware. Our algorithm can be viewed as a practical means to solve the quantum low-rank approximation problem which we formally defined and solved as part of a related work. Alternatively, our algorithm is a generalization of previous VQAs that aimed at learning preparation circuits for pure states. We choose to compile a target mixed state using two types of an ansätze; the first is based on learning a purification of the state and the second on representing it as a convex combination of pure states. In both cases, the resources required to store and manipulate the compiled state grow with the rank of the approximation. Thus, by learning a lower rank approximation of the target state, our algorithm provides a means of compressing a state for more efficient processing. As a byproduct of our algorithm, one effectively learns the principal components of the target state, and hence our algorithm further provides a new method for principal component analysis. We investigate the efficacy of our algorithm through extensive numerical implementations, showing that typical random states and thermal states of many body systems may be learnt this way. Finally, we implement our algorithm on real hardware and show how it can be used to study hardware noise-induced states. |
| 4:45 pm - 5:15 pm | Alicia Magann, Sandia National Laboratories Feedback-based quantum algorithms | Abstract. Variational quantum algorithms (VQAs) are a significant focus of the quantum computing community. These algorithms operate by wrapping a classical optimization loop around a parameterized quantum circuit, and iteratively searching for the parameter configuration that produces the best solution to the problem under consideration. A critical challenge in VQAs is the difficulty of this classical optimization problem, which can become intractable as the number of quantum circuit parameters increases. I will introduce feedback-based quantum algorithms (FQAs) as an alternative paradigm that is optimization-free and applicable to a broad range of applications. Within this paradigm, quantum circuit parameter values are assigned in a layer-wise manner using a deterministic, measurement-based feedback law derived from quantum Lyapunov control principles. The use of feedback in this manner guarantees a monotonic improvement in solution quality with respect to the depth of the quantum circuit. I will overview quantum Lyapunov control theory as a motivation for this framework and go on to discuss concrete formulations of FQAs for applications including quantum simulation and combinatorial optimization. I will conclude by presenting results from a hardware implementation and numerical investigations of convergence, scalability, and robustness. Sandia National Labs is managed and operated by NTESS under DOE NNSA contract DENA0003525. SAND2022-10773 A. |
| 5:15 pm - 5:45 pm | Jacob Watkins, Michigan State University Simulating time-dependent Hamiltonians with finite-dimensional clocks | Abstract. To date, several simulation methods have been proposed that achieve optimal scaling for time-independent Hamiltonians. However, no such algorithm has been developed that saturates these lower bounds for a non-trivial time-dependent Hamiltonian. We solve this problem by providing a new approach for approximating an ordered operator exponential using an ordinary operator exponential acting on a larger, finite-dimensional Hilbert space, which we call a “clock space”. This approach allows us to translate results for simulating time-independent systems to the time-dependent case. Our result solves two open problems in simulation. First, we provide a rigorous way to generate time-dependent product and multiproduct formulas using translations on the clock, constructing a new family of multiproduct formulas for time-dependent Hamiltonians that yield both commutator scaling and poly-logarithmic error. Our construction outperforms existing methods for simulating physically local, time-dependent Hamiltonians. Second, we extend the application of qubitization to time-dependent Hamiltonians and achieve the current best computational scaling for linear time dependencies, matching the value for time-independent qubitization. We show that as the number of auxiliary qubits grows, the error in the ordered operator exponential vanishes, as well as the entanglement between the clock and the system of interest. |
| 5:45 pm - 6:15 pm | Matthias C. Caro, California Institute of Technology Out-of-distribution generalization for learning quantum dynamics and dynamical simulation | Abstract. Generalization bounds are a critical tool to assess the training data requirements of Quantum Machine Learning (QML). In this work, we prove the first out-of-distribution generalization guarantees in QML, where we require a trained model to perform well even on testing data drawn from a distribution different from the training data distribution. Namely, we establish out-of-distribution generalization for the task of learning an unknown unitary using a quantum neural network and for a broad class of training and testing distributions. In particular, we show that one can learn the action of a unitary on entangled states using only product state training data. Since product states can be prepared using only single-qubit gates, this advances the near-term prospects of QML for learning quantum dynamics, and further opens up new methods for both the classical and quantum compilation of quantum circuits. Based on these insights, we propose a QML-based algorithm for simulating quantum dynamics on near-term quantum hardware and rigorously prove its resource-efficiency in terms of qubit and training data requirements. We also demonstrate the viability of this algorithm through numerical experiments, both in classical simulations and on quantum hardware. Finally, we embed this algorithm in a broader framework for using QML methods for quantum dynamical simulation on NISQ devices. |
SESSION 9c: Advance in quantum information theory (Mariposa Meeting Room)Chair: (John DeBrota (UNM)) | |
| 3:45 pm - 4:15 pm | Iman Marvian, Duke University Operational Interpretation of Quantum Fisher Information in Quantum Thermodynamics | Abstract. In the framework of quantum thermodynamics preparing a quantum system in a general state requires the consumption of two distinct resources, namely, work and coherence. It has been shown that the work cost of preparing a quantum state is determined by its free energy. Considering a similar setting, here we determine the coherence cost of preparing a general state when there are no restrictions on work consumption. More precisely, the coherence cost is defined as the minimum rate of consumption of systems in a pure coherent state, that is needed to prepare copies of the desired system. We show that the coherence cost of any system is determined by its quantum Fisher information about the time parameter, hence introducing a new operational interpretation of this central quantity of quantum metrology. Our resource-theoretic approach also reveals a previously unnoticed connection between two fundamental properties of quantum Fisher information. |
| 4:15 pm - 4:45 pm | Shawn Geller, University of Colorado Improving quantum state detection with adaptive sequential observations | Abstract. For many quantum systems intended for information processing, one detects the logical state of a qubit by integrating a continuously observed quantity over time. For example, ion and atom qubits are typically measured by driving a cycling transition and counting the number of photons observed from the resulting fluorescence. Instead of recording only the total observed count in a fixed time interval, one can observe the photon arrival times and get a state detection advantage by using the temporal structure in a model such as a hidden Markov model. We study what further advantage may be achieved by applying pulses to adaptively transform the state during the observation. We give a three-state example where adaptively chosen transformations yield a clear advantage, and we compare performances on an ion example, where we see improvements in some regimes. We provide a software package that can be used for exploration of temporally resolved strategies with and without adaptively chosen transformations. |
| 4:45 pm - 5:15 pm | Arjendu Pattanayak, Carleton College Extreme parametric sensitivity in bath-mediated transport due to avoided level crossings: The dissipative quantum Rabi model and others | Abstract. We show that non-equilibrium steady states (NESS) of the quantum Rabi model subject to two dissipative interactions have transport properties that are enhanced as spikes over narrow parameter windows, with a lineshape that depends on details of the model for the system and the dissipation. We also find similar results for related models of quantum transport and light-matter interactions including the Holstein and Dicke Hamiltonians. We show that this phenomenon is due to low-energy avoided crossings in the corresponding closed system. In particular the transport spikes are correlated with spikes in the entanglement entropy of key energy eigenstates of the closed system, a signature of strong mixing and resonance among system degrees of freedom. Further, by comparing the Quantum Rabi model with the Jaynes-Cummings model we show that this phenomenon is related to quantum integrability. The results seem generically relevant and widely applicable, from analyses of chemical reaction dynamics in the condensed phase to the scrambling of information in well-controlled quantum devices. |
| 5:15 pm - 5:45 pm | Luis Pedro Garcia-Pintos, University of Maryland Joint Quantum Institute Reproducing stochastic quantum trajectories and applications to quantum feedback control | Abstract. I show an explicit construction of a Hamiltonian that, given access to a measurement record, reproduces the stochastic trajectories of a continuously monitored quantum system. This provides a tool to engineer quantum control protocols by exploiting measurement feedback. As examples of this, I will show how to emulate the time-reversed dynamics of an open quantum system and a way to prepare a quantum state. Moreover, via suitably chosen feedback Hamiltonians, I show how to mitigate the production of qubit errors with smaller ancilla overheads than traditional quantum error correction techniques if one has access to the environment responsible for the errors. |
| 5:45 pm - 6:15 pm | Mark Webster, University of Sydney 3 Algorithms for non-Clifford operators of CSS codes | Abstract. Finding fault-tolerant non-Clifford logical operators on stabiliser codes is important for realisation of universal quantum computing. This task is particularly challenging for LDPC codes. The XP formalism allows us to better understand the logical operator structure of stabiliser codes, including logical operators at various levels of the Clifford hierarchy. In this talk, I will present 3 algorithms for finding fault-tolerant non-Clifford logical operators of CSS codes |
SESSION 10: Superconducting quantum computing (Islands Ballroom)Chair: (Tameem Albash (UNM)) | |
| 8:30 am - 9:15 am | Andreas Wallraff, ETH Zurich (invited) Quantum Error Correction in a Surface Code with Superconducting Circuits | Abstract. Superconducting electronic circuits are ideally suited for studying quantum physics and its applications. Since complex circuits containing hundreds or thousands of elements can be designed, fabricated, and operated with relative ease, they are one of the prime contenders for realizing quantum computers. Currently, both academic and industrial labs vigorously pursue the realization of universal fault-tolerant quantum computers. However, building systems which can address commercially relevant computational problems continues to require significant conceptual and technological progress. For fault-tolerant operation quantum computers must correct errors occurring due to unavoidable decoherence and limited control accuracy. Here, we demonstrate quantum error correction using the surface code, which is known for its exceptionally high tolerance to errors. Using 17 physical qubits in a superconducting circuit (see Figure 1) we encode quantum information in a distance-three logical qubit building up on our recent distance-two error detection experiments [1]. In an error correction cycle taking only 1.1 s, we demonstrate the preservation of four cardinal states of the logical qubit. Repeatedly executing the cycle, we measure and decode both bit- and phase-flip error syndromes using a minimum-weight perfect-matching algorithm in an error-model-free approach and apply corrections in postprocessing. We find a low logical error probability of 3 % per cycle [2]. The measured characteristics of our device agree well with a numerical model. Our demonstration of repeated, fast, and high-performance quantum error correction cycles, together with recent advances in ion traps, support our understanding that fault-tolerant quantum computation will be practically realizable. |
| 9:15 am - 9:45 am | Maxime Dupont, Rigetti Computing How hard is it to outperform a classical simulator at running a quantum optimization algorithm? | Abstract. Platforms for studying variational quantum-classical algorithms (VQAs) with superconducting qubit processors reaching beyond the limits of exascale emulation limits are on the horizon. In this talk, we review recent work on one pattern of VQA, the QAOA anstaz. First, we refine expected boundaries for scaling up noisy simulation with QAOA with tensor networks, limited by entanglement. Still, initial states and final solutions with QAOA typically have low entanglement. We thus clarify the evolution of entanglement during the execution of the algorithm. Next, we report QAOA runs on the recent Aspen-M 80Q platform at Rigetti. We highlight the role of error mitigation for tailoring hardware noise at scale. |
| 9:45 am - 10:15 am | Aleksander Kubica, AWS Center for Quantum Computing Erasure qubits: Overcoming the T1 limit in superconducting circuits | Abstract. The amplitude damping time, T_1, has long stood as the major factor limiting quantum fidelity in superconducting circuits, prompting concerted efforts in the material science and design of qubits aimed at increasing T_1. In contrast, the dephasing time, T_\phi, can usually be extended above T_1 (via, e.g., dynamical decoupling), to the point where it does not limit fidelity. In this article we propose a scheme for overcoming the conventional T_1 limit on fidelity by designing qubits in a way that amplitude damping errors can be detected and converted into erasure errors. Compared to standard qubit implementations our scheme improves the performance of fault-tolerant protocols, as numerically demonstrated by the circuit-noise simulations of the surface code. We describe two simple qubit implementations with superconducting circuits and discuss procedures for detecting amplitude damping errors, performing entangling gates, and extending T_\phi. Our results suggest that engineering efforts should focus on improving T_\phi and the quality of quantum coherent control, as they effectively become the limiting factor on the performance of fault-tolerant protocols. |
SESSION 11: Quantum field theory and many-body states (Islands Ballroom)Chair: (Andrew Landahl (Sandia National Lab)) | |
| 10:45 am - 11:30 am | Natalie Klco, Duke University (invited) Quantum simulating (with) an entangled fabric | Abstract. Toward the quantum simulation of lattice gauge theories, we will discuss the many complementary routes for representing continuous fields onto discrete quantum systems, reverberations of such decisions throughout subsequent algorithmic quantum resources, and techniques for reliably protecting symmetries during imperfect dynamical evolution. From multiple perspectives, this will lead to examples of how naturally distributed entanglement in the simulated field can provide practical guidance toward quantum simulation (co)design, both for applications in fundamental physics and for large-scale quantum computations more broadly. |
| 11:30 am - 12:00 pm | Sajant Anand, University of California Berkeley Holographic quantum simulation of entanglement renormalization circuits | Abstract. While standard approaches to quantum simulation require a number of qubits proportional to the number of simulated particles, current noisy quantum computers are limited to tens of qubits. With the technique of holographic quantum simulation, a D-dimensional system can be simulated with a D−1-dimensional subset of qubits, enabling the study of systems significantly larger than current quantum computers. Using circuits derived from the multiscale entanglement renormalization ansatz (MERA), we accurately prepare the ground state of an L=32 critical, non-integrable perturbed Ising model and measure long-range correlations on the 10 qubit Quantinuum trapped ion computer. We introduce generalized MERA (gMERA) networks that interpolate between MERA and matrix product state networks and demonstrate that gMERA can capture far longer correlations than a MERA with the same number of qubits, at the expense of greater circuit depth. Finally, we perform noisy simulations of these two network ansätze and find that the optimal choice of network depends on noise level, available qubits, and the state to be represented. |
SESSION 12: Ion traps and control (Islands Ballroom)Chair: (Anthony Ransford (Quantinuum)) | |
| 1:30 pm - 2:15 pm | Megan Ivory, Sandia National Lab (invited) Photonics-Integrated Microfabricated Surface Traps Trapped-Ion Control and Readout | Abstract. Some of the more advanced systems for quantum applications spanning clocks, sensors, and computers are based on the control and manipulation of atoms using photons. Here, I discuss ongoing efforts at Sandia National Laboratories to leverage microfabricated surface traps and integrated photonics for trapped ion systems, and the unique systematics presented by these integration efforts. In particular, I will present early demonstrations and characterizations of trapped ions utilizing multilayered waveguides for UV and visible/IR light and single photon avalanche detectors integrated with microfabricated surface traps for low size, weight, and power (SWaP) deployable atomic clocks. Sandia National Laboratories is a multimission laboratory managed and operated by National Technology and Engineering Solutions of Sandia, LLC, a wholly owned subsidiary of Honeywell International Inc., for the U.S. Department of Energy's National Nuclear Security Administration under contract DE-NA0003525. |
| 2:15 pm - 2:45 pm | Nathan Lysne, National Institute of Standards and Technology, Boulder Control over a single shared motional quantum between ions in a 2D array | Abstract. Two-dimensional arrays of ions trapped in individually addressable microtraps are promising systems for simulation of many-body phenomena such as spin frustration and bosons evolving in synthetic magnetic fields. Achieving control over not only each ion but also shared motional excitations to study such systems is difficult due to their geometry, susceptibility to noise in the external potential, and competition with motional heating. To realize a minimal such two-dimensional array, we have developed a surface-electrode ‘triangle trap,’ fabricated by Sandia National Labs and operated at cryogenic temperatures. This device creates a triangular array of individual trapping sites spaced 30 µm apart with sufficient degrees of freedom to independently control the motional mode frequencies and orientations of an ion trapped in each potential. In this work, we will first discuss how we control the internal and motional states of individual 9Be+ ions in the array. This toolbox includes a new technique to address and read out selected ions without the need for additional laser beams by selectively inducing micromotion via the same site-specific electric fields used for micromotion compensation. We will then share recent results on coherent operations between adjacent ions in the array, including a demonstration of over 100 exchanges of a single phonon between ions achieved by tuning motional mode frequencies into resonance through control over individual site curvatures. |
| 2:45 pm - 3:15 pm | David Allcock, University of Oregon Controlling trapped-ion motional modes for precision measurement and CVQC | Abstract. Motional modes of trapped ions have been shown to be a useful tool for quantum sensing as well as a platform for performing continuous variable quantum computing (CVQC). Both applications require the ability to prepare well-defined motional states with high fidelity. Many of these states can be generated from motional ground states without the use of laser fields. We report our progress towards generation of one-mode and two-mode squeezed states using parametric excitation. These operations help to create motional state interferometers and can be used to achieve Heisenberg-limited phase sensitivities. We present a preliminary implementation of an SU(1,1) interferometer using two motional modes of a 40Ca+ ion in a Paul trap. To characterize motional states, the ions’ motion is coupled to internal ‘spin’ states, which are distinguishable through spin-dependent fluorescence. Photon scattering causes the ion to recoil, which generally decoheres the ions’ motional modes. This decoherence prevents mid-algorithm measurements, which are necessary for processes that require classical feedback. To address this issue, we describe progress towards the use of ‘protected’ modes (See also P.-Y. Hou et al., arXiv:2205.14841) within chains consisting of an odd number of ions, where the center ion has zero displacement. The protection offered by these ions is measured by analysis of the heating rates and coherence time of the protected mode during scattering events. Support from ARO and NSF. |
SESSION 13: New devices and characterization (Islands Ballroom)Chair: (Mohan Sarovar (Sandia National Lab)) | |
| 3:45 pm - 4:15 pm | Vasileios Niaouris, University of Washington Shallow donor spin-qubits in ZnO - Using ion implantation and focused-ion beam milling for donor formation and photonics integration | Abstract. Neutral shallow donors (D0) in ZnO such as In, Ga, and Al substituting for Zn are promising solid-state spin qubits for quantum technologies. The D0 are optically coupled to donor bound excitons. Studying donor ensembles, we have demonstrated narrow inhomogeneous linewidths (~10GHz), long spin relaxation time (T1, up to 0.48 sec at 1.75 T) [1], spin initialization via optical pumping [2], and all-optical coherent control [3]. In this contribution, we will be discussing the ability to control the number of donors accessed optically via implantation and the potential to use focused ion beam milling (fibbing) to fabricate on ZnO. Through implantation and annealing, we can form In donors within a thin layer of ZnO, with favorable optical and coherent properties. Via fibbing, a slice of different thicknesses, ranging between 0.1 and 3 um, was cut out of the ZnO crystal. Due to the reduced thickness, we can probe smaller ensembles that retain good optical properties (after annealing) and identify candidates for stable single emitters. Combining donor implantation and fibbing, we aim to fabricate photonic structures around implanted donors, a significant step towards scaling this emerging technology. [1] V. Niaouris, et al., Phys. Rev B 105, 195202 (2022) [2] X. Linpeng et al., Phys. Rev. Appl. 10, 064061 (2018) [3] M. L. K. Viitaniemi, et al., Nano Lett. 22, 5 (2022) *Supported by the U.S. DOE (DE-SC0020378), the NSF (1820614), and the Army Research Office MURI Grant (18057522). |
| 4:15 pm - 4:45 pm | Jordan Hines, University of California Berkeley Scaling randomized benchmarking into the quantum advantage regime | Abstract. Randomized benchmarks are widely used for quantifying the performance of quantum processors. However, most existing protocols are limited in scalability, often due to requiring classical computations that scale exponentially in the number of qubits. Here, we introduce two highly scalable randomized benchmarking methods with low classical computation cost. Our methods modify standard randomized benchmarking and cross entropy benchmarking, connecting those methods and preserving their core strengths. Our first method uses randomized mirror circuits to enable benchmarking a large class of universal gate sets. Our second method benchmarks Clifford gates by applying a streamlined fidelity estimation method to random circuits. We use theory, simulations, and experiments to show that our methods reliably estimate the average error rate of random circuit layers. We demonstrate randomized benchmarking of universal gate sets on four qubits of the Advanced Quantum Testbed, including a gate set containing a controlled S gate and its inverse, and we investigate the impact of non-Clifford gates on the observed error rate. Finally, we demonstrate that our methods scale to many qubits with experiments on a 27-qubit IBM Q processor, and quantify the contribution of crosstalk to the error rate. This work was supported in part by the LDRD program at SNL and by the US DOE SC/ASCR’s Quantum Testbeds for Science Program. SNL is managed and operated by NTESS under DOE NNSA contract DE-NA0003525. |
| 4:45 pm - 5:15 pm | Stefan Seritan, Sandia National Laboratories How to benchmark quantum computers using any quantum algorithm | Abstract. Quantum computers promise better solutions to real-world problems, such as those arising in quantum chemistry, but only if they can successfully run large, complex programs implementing specific quantum algorithms. There is thus an urgent need for benchmarks that measure how well quantum computers can execute such programs. However, this appears impossible because quantum programs solving difficult problems are (1) too big to fit on current-generation quantum testbeds, and (2) seemingly impossible to verify on classical computers. We overcome both problems by applying circuit mirroring and subcircuit snipping to generate the first scalable, efficiently verifiable application-inspired volumetric benchmarks. We demonstrate our technique on a key subroutine for quantum chemistry algorithms: the application of a block-encoded second quantized Hamiltonian. While this is more resource intensive than near-term approaches to the same task, it is more representative of what will be executed on future fault-tolerant systems. Experiments were performed for small instances, i.e., minimal basis H2, HeH+, and LiH, using two different fermion-to-qubit mappings. We compare the performance of several IBM Q devices on our application-inspired benchmarks to their performance on prior mirror circuit benchmarks. We also validate our results against simulations using error models containing coherent and stochastic noise. SNL is managed and operated by NTESS under DOE NNSA contract DE-NA0003525. |
SESSION 14: Software for quantum computing (Islands Ballroom)Chair: (Ivan Deutsch (UNM)) | |
| 5:30 pm - 6:15 pm | Dave Bacon, Google (invited) And Yet It Scales! | Abstract. The promise of quantum error correction is that one can reduce the effects of decoherence and noise by encoding information across multiple physical degrees of freedom. A key property of these schemes is that they reduce the noise exponentially as one grows the number of physical subsystems. In this talk I'll discuss the recent experiment we performed at Google that demonstrated this effect. In particular our experiment showed that a distance-5 surface code logical qubit modestly outperforms an ensemble of distance-3 logical qubits on average, both in terms of logical error probability over 25 cycles and logical error per cycle (2.914%\(\pm\)0.016% compared to 3.028\(\pm\)0.023%). |
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