Bulletin of the American Physical Society
APS March Meeting 2022
Volume 67, Number 3
Monday–Friday, March 14–18, 2022; Chicago
Session N34: CV Quantum Computation and Simulation IFocus Recordings Available

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Sponsoring Units: DQI Chair: Kero Lau, Simon Fraser University Room: McCormick Place W193A 
Wednesday, March 16, 2022 11:30AM  12:06PM 
N34.00001: Protecting a bosonic qubit with autonomous quantum error correction Invited Speaker: Chen Wang Quantum error correction is usually implemented via an active schedule of discrete error syndrome measurements and adaptive recovery operations which are hardware intensive and prone to introducing and propagating errors. In this talk, we will discuss our recent experimental demonstration of autonomous quantum error correction (AQEC) by tailoring dissipation within the quantum system*. Our AQEC is realized by a synthetic dissipation operator activated via continuouswave drives only, which stabilizes the photon number parity of a superconducting cavity, hence correcting for the dominant singlephoton loss errors in the system. We will further discuss the role of dissipation engineering as a resourceefficient alternative or supplement to active QEC in bosonic qubits and logic gates. 
Wednesday, March 16, 2022 12:06PM  12:18PM 
N34.00002: Deterministic microwaveoptical transduction based on quantum teleportation Jing Wu, Chaohan Cui, Linran Fan, Quntao Zhuang The coherent transduction between microwave and optical frequencies is critical to interconnect superconducting quantum processors over long distances. However, it is challenging to establish such a quantum interface with high efficiency and small added noise based on the standard direct conversion scheme. Here, we propose a transduction scheme based on continuousvariable quantum teleportation. Reliable quantum information transmission can be realized with an arbitrarily small cooperativity, in contrast to the direct conversion scheme which requires a large minimum cooperativity. We show that the teleportationbased scheme maintains a significant rate advantage robustly for all values of cooperativity. We further investigate the performance in the transduction of complex quantum states such as cat states and GottesmanKitaevPreskill (GKP) states and show that a higher fidelity or success probability can be achieved with the teleportationbased scheme. Our scheme significantly reduces the device requirement, and makes quantum transduction between microwave and optical frequencies feasible in the near future. 
Wednesday, March 16, 2022 12:18PM  12:30PM 
N34.00003: Experimental implementation of paircat code with superconducting microwave circuits(1/2) Akshay Koottandavida, Ioannis Tsioutsios, Shantanu O Mundhada, Nicholas E Frattini, Luigi Frunzio, Michel H Devoret Encoding quantum information in bosonic modes is a promising way to realize errorcorrected logical qubits for fault tolerant quantum computing. In recent years there has been a lot of progress with qubits encoded in catstates of single bosonic modes. However, existing experimental implementations of catstates with superconducting circuits can only efficiently suppress one type of logical errors, either bit flips or phase flips. Interestingly, encoding quantum information on paircat states, which are superpositions of paircoherent states of two bosonic modes, provides a promising pathway towards a fully errorcorrected logical qubit. Drivendissipative processes can stabilize a manifold of paircat states, providing exponential protection against phaseflip errors. Additionally, paircat code also allows for single photon loss detection in either mode, and hence the correction of bit flips, by monitoring the photonnumber difference between them. Advantageously, this errorsyndrome can be continuously measured in a faulttolerant manner without stopping manifold stabilization. Moreover, paircat code can lead to autonomously errorcorrected logical qubits. 
Wednesday, March 16, 2022 12:30PM  12:42PM 
N34.00004: Experimental implementation of paircat code with superconducting microwave circuits (2/2) Ioannis Tsioutsios, Akshay Koottandavida, Shantanu O Mundhada, Nicholas E Frattini, Luigi Frunzio, Michel H Devoret Encoding quantum information in bosonic modes is a promising way to realize errorcorrected logical qubits for fault tolerant quantum computing. In recent years there has been a lot of progress with qubits encoded in catstates of single bosonic modes. However, existing experimental implementations of catstates with superconducting circuits can only efficiently suppress one type of logical errors, either bit flips or phase flips. Interestingly, encoding quantum information on paircat states, which are superpositions of paircoherent states of two bosonic modes, provides a promising pathway towards a fully errorcorrected logical qubit. Drivendissipative processes can stabilize a manifold of paircat states, providing exponential protection against phaseflip errors. Additionally, paircat code also allows for single photon loss detection in either mode, and hence the correction of bit flips, by monitoring the photonnumber difference between them. Advantageously, this errorsyndrome can be continuously measured in a faulttolerant manner without stopping manifold stabilization. Moreover, paircat code can lead to autonomously errorcorrected logical qubits. 
Wednesday, March 16, 2022 12:42PM  12:54PM 
N34.00005: Simulation of dissipative quantum dynamics through an engineered conical intersection Christopher Wang, Nicholas E Frattini, Benjamin J Chapman, Shruti Puri, Steven M Girvin, Michel H Devoret, Robert J Schoelkopf Conical intersections (CIs) are ubiquitous features in quantum chemistry where two molecular potential energy surfaces intersect. Characterized by a breakdown of the BornOppenheimer approximation, they result in strong hybridization between electronic and nuclear motion. CIs enable nonadiabatic transitions between electronic states and may heavily influence outcomes of chemical reactions via wave packet branching. Engineering synthetic CIs with tunable control to systematically explore the parameter space is a promising application of quantum simulators. In this talk, we report experimental results on controlling and measuring wave packet dynamics through an engineered CI in a superconducting circuit with one nonlinear (electronic) and two linear (nuclear, one reactive and one bath) modes. We characterize the measurement induced dephasing of the qubit via the bath mode, which drives wave packet branching in our model, and demonstrate the influence of excited state dynamics of the reactive mode on the effective dephasing rate in the presence of the CI. Specifically, we show that the dephasing, and hence the branching ratio, is influenced via a competition between the noise from the bath and the reorganization energy of the reactive coordinate. 
Wednesday, March 16, 2022 12:54PM  1:06PM 
N34.00006: Fast flux control of a highQ 3D multimode cavity Riju Banerjee, Srivatsan Chakram, Andrew Oriani, Fang Zhao, Kevin He, Ankur Agrawal, David Schuster Due to their long coherence times and ability to support strong superconductingqubitmediated interactions, 3D microwave cavities have established themselves as an excellent platform for circuit QED experiments. While magnetic fields serve as an important control knob for qubit frequencies and interactions in planar circuits, fast magnetic control of qubits in highcoherence 3D architectures is an outstanding challenge. The introduction of magnetic fields and flux bias lines without sharp reductions in quality factors and coherence times of the cavities requires careful engineering. In this talk, we present a design to introduce a fast flux bias line in highQ 3D multimode systems without compromising on coherence. We also present a threewave mixing scheme that uses RF flux pulses to swap photonic states between different cavities. Our results demonstrate a path to achieve fast control over long lived states in 3D microwave cavities using localized magnetic fields. 
Wednesday, March 16, 2022 1:06PM  1:18PM 
N34.00007: Chiral cavity quantum electrodynamics in a 3D microwave lattice coupled to a transmon qubit Margaret G Panetta, Clai Owens, Brendan Saxberg, Gabrielle Roberts, Srivatsan Chakram, Ruichao Ma, Andrei Vrajitoarea, Jonathan Simon, David Schuster Recent advancements in superconducting quantum systems have created an exciting opportunity to construct from the ground up quantum materials hosting rich interactions. We explore cavity quantum electrodynamics of a superconducting transmon qubit strongly coupled to a lattice of 3D microwave resonators engineered to host a synthetic magnetic field for photons. This metamaterial is the first photonic topological lattice platform compatible with strong interactions. We share recent results [1]: we demonstrate transport in the spectrally distinct chiral edge channels of this system, employ strong transmonlattice coupling to count photons in lattice edge modes, and observe the Lamb shift on the qubit from the synthetic vacuum of the lattice spectrum. We further discuss progress towards measurements with two transmons coupled to this topological photonic material, a setup which should enable quantum communication in chiral lattice edge channels and represent a step towards engineering topological manybody physics for photons. 
Wednesday, March 16, 2022 1:18PM  1:30PM 
N34.00008: Simulation of the SuSchriefferHeeger model using a superconducting parametric cavity Dmytro Dubyna, Jamal Busnaina, Zheng Shi, Jimmy ShihChun Hung, Ibrahim Nsanzineza, Christopher Wilson While largescale universal quantum computers are on the way, analog quantum simulators (AQSs) can be used right now to study complex natural phenomena. By simulating the SuSchrieffer–Heeger (SSH) model that describes particles hopping on a onedimensional lattice with staggered hopping amplitudes, we demonstrate that superconducting parametric cavities are a versatile platform for programable AQS. Our device is a 100 mmlong superconducting quarterwave coplanar waveguide resonator which is shorted by an asymmetrical Superconducting Quantum Interference Device (SQUID). Multiple resonant modes of the cavity are used as a photonic lattice arrayed in a synthetic dimension. Parametric couplings between sites are generated by pumping the SQUID with microwave signals at the difference frequencies of pairs of modes. We perform transport measurements that allow us to reconstruct the full scattering matrix of the SSH chain, observing many of the features of the SSH model. For instance, depending on the ratio between hopping amplitudes and the site number parity, we can observe 0, 1 and 2 edge states which live within the bulk energy gap of the system. Complementary to our published work on the bosonic Creutz ladder [1], this result highlights the power and programmability of superconducting parametric cavities for quantum simulation. 
Wednesday, March 16, 2022 1:30PM  1:42PM 
N34.00009: Engineering arbitrary twomode CV gates with fixed twomode interfaces PakTik Fong, Jason (Sheung Chi) Poon, HoiKwan Lau We explore the possibility to engineer twomode continuousvariable (CV) gates by cascading multiple fixed twomode linear interfaces. We first categorize every gate by its transmission strength, which is invariant under local operations. We show that combining any two interfaces with appropriate singlemode operations in between can arbitrarily alter the transmission strength, thus can engineer arbitrary twomode CV gate. Our protocol requires squeezing on only one of the modes, so it is applicable to platforms with limited controllability. Additionally, we prove that it is generally insufficient to engineer a perfect transducer with two arbitrary interfaces, but always possible with three. It is the theoretical scheme with the minimum resources. 
Wednesday, March 16, 2022 1:42PM  1:54PM 
N34.00010: Multipartite entanglement in a microwave frequency comb Juan Carlos Rivera Hernández, Shan W Jolin, David B Haviland, Ingrid Strandberg, Jose Aumentado, Gustav Andersson The entanglement of multiple, classically distinct states lies at the heart of quantum communication and information processing. In the microwave regime with superconducting circuits, significant progress has been made with multipartite entanglement of discrete qubits, but continuous variable (CV) systems may provide another scalable path toward generation and control of entanglement in large ensembles. For instance, large CV entangled states have been generated in optics by pumping optical parametric oscillators (OPO). Working with microwave and superconducting circuits may provide additional advantages, such as digital electronics and a strong tunable nonlinearity in the Josephson junction. In this work, we measure up to 64 correlated modes propagating in a transmission line connected to a Josephson parametric amplifier (JPA) using a multifrequency digital signal processing methodology, verifying full inseparability between 7 modes. The correlations are achieved by applying a bichromatic pump to the JPA at roughly double its resonance frequency. Our method provides a clear path for scaling to more modes and maybe eventual generation of CV cluster states. 
Wednesday, March 16, 2022 1:54PM  2:06PM 
N34.00011: Combined Dissipative and Hamiltonian Cat Qubit Confinement Ronan Gautier, Mazyar Mirrahimi, Alain Sarlette Quantum error correction with biasednoised qubits can drastically reduce the hardware overhead for universal and faulttolerant quantum computation. In particular, cat qubits feature an exponential error bias thanks to their nonlocal encoding in the phase space of a quantum harmonic oscillator, and are thus a promising kind of biased noise qubits. To confine the state of an oscillator to the cat qubit manifold, two main approaches exist: a Kerrbased conservative confinement with high gate performances, and a dissipative confinement with robust protection to thermal and dephasing noise. Here, we introduce a combined dissipative and Hamiltonian to benefit from the best of both worlds. 
Wednesday, March 16, 2022 2:06PM  2:18PM 
N34.00012: AKLT ground state in "Bosonic Qiskit" Eleanor Crane, Kevin C Smith, Timothy Stavenger, Christopher Kang, Nathan Wiebe, Steven M Girvin A collaboration within the Codesign Center for Quantum Advantage (C2QA) is currently building an instruction set architecture for hybrid qubit/oscillator circuit QED hardware using Qiskit, the IBM opensource software development kit (SDK). Qiskit has been designed to operate on twolevel systems. The aim is to create a branch of Qiskit called "Bosonic Qiskit" which can accommodate continuous variable systems with a view to using "Bosonic Qiskit" to represent circuit QED hardware in the future. As a proof of concept of "Bosonic Qiskit", we use it to implement a symmetry protected topological state  the seminal AKLT chain  using the native bosonic operations made available in the SDK. 
Wednesday, March 16, 2022 2:18PM  2:30PM 
N34.00013: MixedInteger Programming by Continuous Variable Quantum Computation Farhad Khosravi, Artur Scherer, Pooya Ronagh We propose a continuousvariable quantum computation (CVQC) approach to solving mixedinteger programming problems using a circuitmodel quantum optical device. Our strategy is to use the photon number operator associated with each optical mode in the device to encode the integer variables of an optimization problem, and the corresponding quadrature operators to encode the continuous variables of it. Following an adiabatic groundstate preparation scheme, optimal integer and continuous variable solutions are obtained by respectively performing photon number resolving detection and homodyne measurements on the corresponding modes. We demonstrate our method by studying its application to a wide range of important optimization problems, including integer linear and nonlinear programming, continuous nonlinear programming, and mixedinteger programming problems, using realworld instances of these optimization problems such as the integer knapsack problem, the maximum clique problem, and various instances of sparse optimization problems. 
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