SQuInT 2022 Program
Full Program | Thursday | Friday | Saturday | All Sessions | Posters | Talks
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 |
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SQuInT Chief Organizer
Akimasa Miyake, Associate Professor
amiyake@unm.edu
SQuInT Co-Organizer
Hartmut Haeffner, Associate Professor, UC Berkeley
hhaeffner@berkeley.edu
SQuInT Administrator
Dwight Zier
d29zier@unm.edu
505 277-1850
SQuInT Program Committee
Alberto Alonso, Postdoc, UC Berkeley
Philip Blocher, Postdoc, UNM
Neha Yadav, Postdoc, UC Berkeley
Cunlu Zhou, Postdoc, UNM
SQuInT Founder
Ivan Deutsch, Regents' Professor, CQuIC Director
ideutsch@unm.edu
