Bulletin of the American Physical Society
APS March Meeting 2018
Volume 63, Number 1
Monday–Friday, March 5–9, 2018; Los Angeles, California
Session V33: Error Correction with Superconducting QubitsFocus

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Sponsoring Units: DQI Chair: Andrew Cross, IBM T J Watson Res Ctr Room: LACC 408B 
Thursday, March 8, 2018 2:30PM  3:06PM 
V33.00001: Filling cavities to prevent decay: bosonic quantum error correction Invited Speaker: Victor Albert Continuousvariable quantum information processing is a field concerned with using one or more harmonic oscillators to protect, manipulate, and transport quantum information. As opposed to building systems out of twolevel components (qubits), here the minimal component is the phase space associated with a canonical pair of continuous variables — position and momentum for a mechanical oscillator or quadrature components for an electromagnetic field mode. The large Hilbert space describing this phase space allows one to encode information such that recovery from errors is possible, thereby providing competitive alternatives to encoding into a register of qubits. Moreover, we are at the point of realizing fullfledged protocols utilizing such encodings due to significant advances in microwave cavity, atomic ensemble, and trapped ion control. This presentation overviews continuousvariable quantum errorcorrecting codes, from theoretical capabilities to experimental realizations. 
Thursday, March 8, 2018 3:06PM  3:42PM 
V33.00002: Dissipation as a resource for stabilizing quantum states with superconducting qubits Invited Speaker: Mazyar Mirrahimi Recent advances in quantumlimited amplification have opened doors to highfidelity nondemolition measurement of superconducting qubits and have already led to successful experiments on closedloop control of such systems. However, the finite bandwidth of the amplification procedure, together with the timeconsuming data acquisition and posttreatment of the output signal, lead to important latency in the feedback procedure. Alternatively, the reservoir (dissipation) engineering circumvent the necessity of a realtime data acquisition, signal processing and feedback calculation. Coupling the quantum system to be stabilized to a strongly dissipative ancillary quantum system allows us to evacuate the entropy of the main system through the dissipation of the ancillary one. I will overview some theoretical proposals as well as the related experiments through the past few years illustrating the power of such autonomous feedback schemes for stabilizing highly nonclassical states as well as for quantum error correction. 
Thursday, March 8, 2018 3:42PM  3:54PM 
V33.00003: Error Model for Cat States in Superconducting Kerr Nonlinear Resonators Lucas StJean, Pavithran Iyer, Anirudh Krishna, Shruti Puri, Alexandre Blais Quantum error correction protocols require up to thousands of physical qubits per logical qubit in order to protect quantum information from unavoidable errors. A hardware efficient solution is therefore essential for the realization of quantum computers due to the challenge of creating and controlling a high number of qubits. A particularly attractive approach to realize these ideas is using cat states in microwave cavities. I will first summarize a scheme based on twophoton driven Kerr nonlinear resonators for stabilizing cat states [1] and then discuss the error model within this scheme. This model based on photon loss has the interesting property of being biased: photon loss leads to errors close to a ‘bit flip’ error on the cat states subspace while ‘phase flip’ errors are suppressed. Optimizing quantum error correction to take advantage of biased errors has the potential to significantly decrease the number of qubits required by error correction protocols. 
Thursday, March 8, 2018 3:54PM  4:06PM 
V33.00004: Optimizing state stabilization and passive error correction using timevarying dissipation David Rodriguez Perez, Eliot Kapit Tunable couplings between high coherence quantum objects and lossy resonators is a promising approach to state stabilization. However; both analytical and numerical analyses of simple continuous implementations of this technique show that the residual error of the state with increasing lifetime T_{1} scales as (U / T_{1})^{1/2}, where U is the energy penalty for offresonant errors generated by the coupling. We propose the addition of a lossy resonator that is itself parametrically coupled to the first (higher coherence) resonator or qubit. Using numerically optimized pulses coupling between the quantum state and the first (higher coherence) resonator, we use the tunable coupling between the first and second resonators to flush out any occupied states from the error correcting mechanism, and report a steady state residual error scaling of about U / T_{1}, which is optimal given realistic experimental constraints. We demonstrate such improved scaling for the stabilization in both simple singlequbit states, and more complex passive quantum error correction circuits. 
Thursday, March 8, 2018 4:06PM  4:18PM 
V33.00005: Pitch & Catch I: Deterministic State Transfer and Entanglement Between Remote Cavity Quantum Memories Luke Burkhart, Christopher Axline, Wolfgang Pfaff, Mengzhen Zhang, Kevin Chou, Philippe CampagneIbarcq, Philip Reinhold, Luigi Frunzio, Steven Girvin, Michel Devoret, Liang Jiang, Robert Schoelkopf Large quantum machines can benefit from a network architecture, where quantum communication channels between wellisolated subsystems are controlled on demand. One efficient communication scheme is direct, deterministic photon transfer as proposed in [1]. Utilizing RFcontrolled parametric conversion, we realize this protocol between two remote millisecondlifetime microwave cavity memories. We transfer a quantum bit between memories with high efficiency, achieving an average state fidelity that exceeds the classical bound. Furthermore, we extend this scheme in order to halftransfer a photon, generating highfidelity entanglement between the two remote cavities. [1] Cirac et al, PRL 78 3221 1997 
Thursday, March 8, 2018 4:18PM  4:30PM 
V33.00006: Pitch & Catch II: ErrorCorrectable MultiPhoton State Transfer Christopher Axline, Luke Burkhart, Wolfgang Pfaff, Mengzhen Zhang, Kevin Chou, Philippe CampagneIbarcq, Philip Reinhold, Luigi Frunzio, Steven Girvin, Michel Devoret, Liang Jiang, Robert Schoelkopf Direct quantum state transfer suffers from photon loss in the transmission channel. Parametric conversion between microwave cavity memories and propagating photons allows for the deterministic transmission of multiphoton quantum states. These states can be made robust to photon loss. We encode a qubit within a subspace of definite parity—an errorcorrectable encoding—and transfer the state between memories. We measure the transfer efficiency to be at a level where parity measurement and feedback would improve the average state fidelity. With modest technical improvements, we expect to reach a regime where this error detection and correction yields a fidelity exceeding that already achieved for a singlephoton encoding. 
Thursday, March 8, 2018 4:30PM  4:42PM 
V33.00007: Proposal for a Logical Qubit Encoded into a Stabilized Manifold in Two Bosonic Modes. Victor Albert, Shantanu Mundhada, Alexander Grimm, Steven Touzard, Michel Devoret, Liang Jiang We introduce a drivendissipative twomode bosonic system whose reservoir causes simultaneous loss of two photons in each mode and whose steady states are superpositions of BarutGirardello paircoherent states. Quantum information encoded in a manifold spanned by these states is exponentially immune to phase drifts (cavity dephasing) in both modes. It is also possible to protect the encoded information from photon loss in either mode by continuously monitoring an error syndrome given by the photon number difference of the two modes. Furthermore, this monitoring can be done with current circuit QED technology without turning off the dissipative stabilizing process. In this talk, we will briefly introduce the general concept of this approach to quantum error correction as well as the specific encoding used. An overview of a potential implementation for this system in the framework of circuit QED will also be presented. 
Thursday, March 8, 2018 4:42PM  4:54PM 
V33.00008: Constructing optimized bosonic quantum codes via phase alteration Linshu Li, Victor Albert, Kyungjoo Noh, Changling Zou, Liang Jiang Bosonic quantum codes, such as cat codes and binomial codes, can address the key issue of correcting excitation loss in bosonic systems. Typically, there exists a basis for the codewords consisting of excitation probability amplitudes which are all real and positive. We argue that, by utilizing the phase degree of freedom in such probability amplitudes, improved orthogonality between logical states after the error process can be achieved. In particular, we show that a phase alteration of cat codes and binomial codes leads to much improved correction of photon losses, and can be experimentally implemented via a Kerr Hamiltonian. We discuss some extensions showing the general applicability of this principle in designing good quantum codes. 
Thursday, March 8, 2018 4:54PM  5:06PM 
V33.00009: Towards sufficiently fast quantum error correction Austin Fowler We give an update on progress towards a sufficiently fast quantum error correction system to service an array of superconducting qubits. 
Thursday, March 8, 2018 5:06PM  5:18PM 
V33.00010: Properties of a Protected Qubit based on the Superconducting Current Mirror Andy C. Y. Li, Jens Koch Protected quantum circuits are promising candidates to serve as building blocks of faulttolerant universal quantum computers. One of these designs has been proposed to implement a protected qubit based on two Josephson junction chains with strong interchain capacitive coupling and forming a Moebius strip [1]. In this talk, we present a full circuit analysis to investigate the lowenergy spectrum of the device, and the susceptibility to charge and flux noise. Our analytical and numerical studies elucidate the promised protection, motivate practical control protocols, and hence pave the way for the first experimental realization of the design. 
Thursday, March 8, 2018 5:18PM  5:30PM 
V33.00011: Preparation and Readout Methods for Noise Protected Superconducting Qubits David Ferguson, Andy C. Y. Li, Jens Koch Protected quantum circuits are promising candidates to serve as the building blocks of faulttolerant universal quantum computers. However, initialization and readout of noise protected superconducting qubits presents a fundamental challenge to their experimental demonstration. In this talk, we present concepts for preparation and readout methods that would allow for experimental demonstration of enhanced coherence of a noise protected qubit, where the enhanced coherence is enabled by reduced sensitivity to environmental noise. 
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