SQuInT 2021 Program

SESSION 4: Talks at Zoom

10:00am-10:30amVladan Vuletić , Massachusetts Institute of Technology
Entangled optical atomic clock
Abstract Entangled states of many particles can be used to overcome limits on measurements performed with ensembles of independent atoms (standard quantum limit). A particularly simple form of entanglement is spin squeezing, where the quantum noise for the variable of interest, e.g., the phase of an atomic clock, is redistributed into another variable. Spin squeezing can be generated by coupling the atomic ensemble to an optical cavity. We report the first sizeable spin squeezing in an optical-clock atom, ytterbium. The squeezing is generated in the electronic ground state, and then transferred onto the clock transition via the clock laser. I will also discuss new results where we create more complex entangled states via atom-cavity interaction, including an effective time-reversal protocol for a many-body Hamiltonian.
10:30am-10:50amJacob Bringewatt, University of Maryland Joint Quantum Institute
Measuring Functions with Quantum Sensor Networks
Abstract We study the problem of optimally measuring analytic functions of field amplitudes with quantum sensor networks with a focus on the effects of interdependence between the various quantities involved in the measurement scheme. We consider such interdependence both at the level of correlations between field amplitudes [Qian et. al., Phys. Rev. A. 103, L030601 (2021)] and at the level of correlations between the functions of these field amplitudes we seek to measure [Bringewatt et. al., Phys. Rev. Res. 3, 033011 (2021)]. In either case, correlations enable more freedom in choosing measurement protocols relative to simpler formulations of the problem. Taking advantage of this interdependence involves common mathematical themes related to the optimal choice of a basis for the problem at hand and reveals connections between ultimate information theoretic bounds and their saturating protocols via linear programming. In addition, our work greatly expands the scope of such protocols to practically relevant settings.
10:50am-11:10amDiego Barberena, University of Colorado JILA
Quantum-enhanced sensing of displacements and electric fields with large trapped-ion crystals
Abstract In this talk we will describe a protocol that performs quantum enhanced sensing of displacements and electric fields in a large crystal of trapped ions (N=150). The protocol uses the center of mass vibrational mode (COM) of the crystal as a high-Q mechanical oscillator and the ions' collective electronic spin, as the effective measurement device. It is implemented by the use of properly detuned laser beams that entangle the oscillator and the collective spin before applying a weak displacement to the oscillator. After a many-body echo that maps the displacement into a spin rotation while canceling both quantum back-action and thermal noise the collective spin is measured. We derive an effective model of coupled oscillators to describe both the spins and the COM of mode and show that the spin-boson entanglement at the core of the protocol can be understood as the squeezing dynamics of this pair of oscillators. We achieve a sensitivity to displacements of 8.8 ± 0.4 dB below the standard quantum limit and about 19 dB below relevant thermal bounds, and a sensitivity for measuring electric fields of 240 ± 40 nV/m in 1 second (240 nVm-1Hz-1/2). With future improvements, electric field sensitivities below 1 nV/m may be possible, which could enable searches for dark matter.
11:10am-11:30amChenxu Liu, Virginia Tech
Protocols for robust generation of microwave photonic graph states from superconducting qubits
Abstract We present protocols that use superconducting qubits for the robust generation of microwave photon cluster and graph states. We consider both fixed-frequency and tunable-frequency transmon qubits as microwave photon emitters and provide the photonic graph state generation circuits. We compare four microwave photonic encoding methods and estimate the photonic graph state fidelity. The generated highly entangled states can be tailored to various quantum information processing tasks, such as robust quantum communication and entanglement generation between different modules of a distributed superconducting qubit processor.
11:30am-11:50amXiaoyue Jin, National Institute of Standards and Technology, Boulder
A versatile parametric coupler between two transmon qubits
Abstract Parametric coupling is a powerful tool that can be used to generate tunable coupling between superconducting qubits via a microwave pump. In this talk, we demonstrate a versatile parametric coupler between two transmon qubits, which can be used to eliminate the residual ZZ coupling between the qubits, to realize a cZ gate by on-resonant parametric coupling, as well as a new kind of cZ gate by off-resonant parametric ZZ manipulation. In the residual ZZ coupling elimination experiment, we show that the upper limit of the effective ZZ coupling after elimination is nominally zero, with an experimental upper limit of 1-10 kHz. Randomized benchmarking experiments show that the on-resonant cZ gate has a fidelity of 99.4% with a gate time of 60 ns, whereas the off-resonant cZ gate has a fidelity of 99.5% with a gate time of 30 ns. We show the gate time dependence of the fidelities of both types of cZ gates and discuss the source of error for those gates.

SQuInT Chief Organizer
Akimasa Miyake, Associate Professor

SQuInT Co-Organizer
Brian Smith, Associate Professor

SQuInT Local Organizers
Philip Blocher, Postdoc
Pablo Poggi, Research Assistant Professor
Tzula Propp, Postdoc
Jun Takahashi, Postdoc
Cunlu Zhou, Postdoc

SQuInT Founder
Ivan Deutsch, Regents' Professor, CQuIC Director

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