Bulletin of the American Physical Society
APS March Meeting 2019
Volume 64, Number 2
Monday–Friday, March 4–8, 2019; Boston, Massachusetts
Session S27: Landauer-Bennett Award Session: Quantum Error Correction Theory and Experiment IIIFocus
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Sponsoring Units: DQI Chair: Markus Kesselring Room: BCEC 160C |
Thursday, March 7, 2019 11:15AM - 11:51AM |
S27.00001: Rolf Landauer and Charles H. Bennett Award in Quantum Computing talk: Repeated parity measurement and feedback in a mixed-species trapped ion register Invited Speaker: Jonathan Home Quantum error correction is essential for realizing the full potential of large-scale quantum information processing devices. Fundamental to its experimental realization is the repetitive detection of errors via projective measurements of quantum correlations among qubits, as well as corrections using conditional feedback. I will describe experiments in which we demonstrate up to 50 sequential measurements of correlations between two beryllium ion microwave qubits using an ancillary optical-frequency qubit in a calcium ion, and implement feedback that allows us to stabilize two-qubit subspaces as well as maximally entangled Bell states [1]. The use of multiple ion species allows us to completely reset the ancilla after measurement and completely mitigate any unwanted effects. Looking towards further scaling, many apparent challenges appear to lie in the use of radio-frequency traps, including power-dissipation and the need to co-align microscopically varying potentials. I will describe how this might be mitigated using micro-fabricated arrays of Penning traps, which would also provide a powerful tool for implementing trapped-ion quantum simulation on a variety of two-dimensional lattices. |
Thursday, March 7, 2019 11:51AM - 12:03PM |
S27.00002: Optimality of Gottesman-Kitaev-Preskill (GKP) Codes for Bosonic Quantum Error Correction Kyungjoo Noh, Victor Albert, Liang Jiang Bosonic quantum error correction has recently risen as a hardware-efficient alternative to the conventional multi-qubit-based quantum error correction. We mainly focus on photon loss error, which is a dominant error source in microwave cavity modes. Previously, it was shown that GKP codes outperform many other bosonic quantum error-correcting codes in correcting photon loss errors, despite the fact that GKP codes are not designed to correct loss errors [1]. Here, we explain why GKP codes perform well against photon loss errors by providing a near-optimal decoding scheme and analyzing its performance. Furthermore, we formulate a biconvex optimization to find the best single-mode bosonic error-correcting code for photon loss errors. In particular, we solve the biconvex optimization heuristically by an alternating semi-definite programming method and show that, starting from Haar random initial codes, our numerical optimization yields a hexagonal GKP code as an optimal encoding in a practically relevant regime [2]. |
Thursday, March 7, 2019 12:03PM - 12:15PM |
S27.00003: High-threshold fualt-tolerant quantum computation with GKP qubits and realistically noisy devices Kosuke Fukui, Akihisa Tomita, Keisuke Fujii To implement fault-tolerant quantum computation with continuous variables, the Gottesman-Kitaev-Preskill (GKP) qubit has been recognized as an important technological element. We have proposed a method to reduce the required squeezing level to realize large scale quantum computation with the GKP qubits [Phys. Rev. X. 8, 021054 (2018)]. Although our method can reduce the required squeezing level to less than 10 dB, which is within the reach of the current experimental technology, we have assumed that the CZ gate and an efficiency of the homodyne detection are ideal. In this work, we show that the required squeezing level is around 10 dB under the realistic assumption that the CZ gate and homodyne detection degrade the squeezing level of the GKP qubits, developing a method to reduce a noise on the GKP qubit by using postselection and maximum-likelihood methods. |
Thursday, March 7, 2019 12:15PM - 12:27PM |
S27.00004: Grid states for encoding and stabilizing a logical qubit in superconducting circuits (Part 1) Alec Eickbusch, Steven Touzard, Phillipe Campagne-Ibarcq, Evan Zalys-Geller, Nicholas Frattini, Volodymyr Sivak, Shruti Puri, Mazyar Mirrahimi, Shyam Shankar, Michel H. Devoret Quantum computation requires that systems preserve quantum information in the presence of noise. The impact of this noise can be mitigated by redundantly encoding a quantum bit of information within a space with a large number of dimensions. Stabilization is done by detecting noise-induced transformations of the system state before the encoded information is lost. In 2001, Gottesman Kitaev and Preskill (GKP) proposed to encode a quantum bit in non-local grid states of a harmonic oscillator. Remarkably, GKP codes have the potential to protect quantum information against all known error channels. In this talk, I will review GKP code properties and present a protocol based on a tunable interaction with an ancillary two-level system to create and stabilize GKP grid states using phase-estimation of the harmonic oscillator field. |
Thursday, March 7, 2019 12:27PM - 12:39PM |
S27.00005: Grid states for encoding and stabilizing a logical qubit in superconducting circuits (Part 2) Steven Touzard, Alec Eickbusch, Phillipe Campagne-Ibarcq, Evan Zalys-Geller, Nicholas Frattini, Volodymyr Sivak, Shruti Puri, Mazyar Mirrahimi, Shyam Shankar, Michel H. Devoret Protecting quantum information requires encoding a quantum bit of information into a space with a large number of dimensions. To this end, Gottesman Kitaev and Preskill (GKP) proposed to use a single harmonic oscillator as an alternative to an ensemble of many two-level systems. In this scheme, the information is encoded in grid states of the oscillator. The dispersive interaction between the oscillator and an ancillary two-level system is sufficient to create and stabilize these non-local states, provided that the interaction strength is periodically modulated in time. In this talk, I will show how to engineer such a modulated interaction and I will present our experimental progress towards the creation and stabilization of GKP grid states. |
Thursday, March 7, 2019 12:39PM - 12:51PM |
S27.00006: Continuous symmetries and approximate quantum error correction Philippe Faist, Sepehr Ghazi Nezami, Victor Albert, Grant Salton, Fernando Pastawski, Patrick Hayden, John Preskill Quantum error correction and symmetries are relevant to many areas of physics, including many- body quantum systems, holographic quantum gravity, and reference-frame error-correction [Hayden et al., arXiv:1709.04471]. Here, we show that any code is fundamentally limited in its ability to approximately error-correct against erasures at known locations if it is covariant with respect to a continuous local symmetry. Our bound vanishes either in the limit of large individual subsystems, or in the limit of a large number of subsystems, and is approximately tight in these regimes. Furthermore, we prove an approximate version of the Eastin-Knill theorem that quantifies a code’s ability to correct erasure errors if it admits a universal set of transversal logical gates. The bound is in terms of the local physical subsystem dimension. We provide a collection of example codes illustrating our bounds in different regimes. In the context of the AdS/CFT correspondence, our approach provides insight into how time evolution in the bulk corresponds to time evolution on the boundary without violating the Eastin-Knill theorem, and our five-rotor code can be stacked to form a covariant holographic code. |
Thursday, March 7, 2019 12:51PM - 1:03PM |
S27.00007: Numerically optimized quantum error-correcting codes for a bosonic mode Matti Silveri, Kari Mäkinen Bosonic quantum error-correcting codes, such as cat and binomial codes, provide good performance against photon loss errors and are experimentally realizable e.g. with superconducting circuits. Motivated by this and aiming to broaden the spectrum of bosonic codes, we have numerically searched for bosonic single-mode codes. The codes are constructed from a finite superposition of Fock states. By utilizing numerical methods, the complex coefficients of the Fock states are chosen so that a code protects against L photon loss errors and minimizes the probability for the L+1:th error to occur. We have found codes that are protected up 9 photon loss errors. We present the structure and analyze the performance of these numerically optimized codes. |
Thursday, March 7, 2019 1:03PM - 1:15PM |
S27.00008: Single-mode bosonic error correcting codes with rotation symmetry Arne Grimsmo, Joshua Combes, Ben Q Baragiola Bosonic mode error correcting codes, or mode codes for short, are error correcting codes where a qubit (or qudit) is encoded into one or multiple bosonic modes, i.e., quantum oscillators with an infinite Hilbert space. In this talk I focus on single-mode codes that obey rotation symmetry in phase space, such as the the well known Cat-, Binomial- and GKP codes. I will introduce a universal scheme for this class of codes based only on simple and experimentally well-motivated interactions. The scheme is fault-tolerant in the sense that small errors are guaranteed to remain small under the considered gates. I will also introduce a fault-tolerant error correction scheme based on cross-Kerr interactions and destructive phase measurement (e.g., heterodyne). Remarkably, the error correction scheme approaches the optimal recovery map for Cat and Binomial codes when the ancilla modes are error free. We numerically compute break-even thresholds under loss and dephasing, both with ideal and faulty ancillas. |
Thursday, March 7, 2019 1:15PM - 1:27PM |
S27.00009: Simplified mixed-state encoding for quantum computation with continuous-variable systems Kevin Marshall, Daniel James, Alexandru Paler, Hoi-Kwan Lau Recent development of mixed-state encoding (MSE) allows a pure-state logical qubit to be encoded by a continuous-variable system in mixed physical state. Despite interest due to its counter-intuitiveness, the utility of current MSE is limited due to several operational drawbacks, namely probabilistic initialisation, redundant information carrier, and requirement of discrete-variable measurement. In this work, we present a simplified MSE that does not suffer from any of these drawbacks. Specifically, our protocol encodes each qubit by only one mixed-state harmonic oscillator, and the logical basis can be deterministically initialised by displacing a thermal equlibirum state. By using measurement-based quantum computation formalism, logical operations can be performed by only continuous-variable interaction and measurement. Without the necessity of ground state cooling, our proposal could broaden the candidate for quantum computation, and reduce the re-initialisation time of measured qubits. Additionally, the noise tolerance of logical quantum information can be enhanced by treating conventional pure-state encoded qubits as MSE qubits. |
Thursday, March 7, 2019 1:27PM - 1:39PM |
S27.00010: Fault-tolerant gates on a logical qubit Serge Rosenblum, Philip Reinhold, Wenlong Ma, Liang Jiang, Luigi Frunzio, Robert J Schoelkopf A fault-tolerant architecture based on error-corrected qubits requires the implementation of logical gates that do not induce uncorrectable errors. Here, we present a fault-tolerant construction for a gate on a cavity-encoded logical qubit. The scheme uses the multilevel structure of a transmon ancilla, along with RF-tunable transmon-cavity interaction, to apply arbitrary phases to the cavity Fock states. This enables a broad range of gates on a variety of encodings, while protecting the logical qubit against photon loss, as well as ancilla decay and dephasing. Together with the previously demonstrated fault-tolerant syndrome measurements [1], this result further expands the toolbox towards fully fault-tolerant processing of logical qubits. |
Thursday, March 7, 2019 1:39PM - 1:51PM |
S27.00011: Optimal condition for a cavity QED-based fault-tolerant quantum computation Rui Asaoka, Rina Kanamoto, Yuuki Tokunaga, Takao Aoki Cavity quantum electrodynamics (QED) has been extensively studied for decades as one of the promising candidates for the realization of quantum computing and quantum network. For example, the controlled phase flip gate between photons assisted by cavity-QED systems was proposed in 2004[1] and demonstrated recently[2]. However, fault-tolerant quantum computing is still difficult because of the infidelity and the losses originated from imperfections of the cavity QED system. |
Thursday, March 7, 2019 1:51PM - 2:03PM |
S27.00012: Simulation of Gaussian channels via teleportation with applications to error correction and secret-key capacities. Spyros Tserkis, Josephine Dias, Riccardo Laurenza, Samuel L Braunstein, Stefano Pirandola, Timothy Ralph Gaussian channels are the typical way to model the decoherence in continuous-variable quantum states. It is known that those channels can be simulated by a teleportation protocol using as a resource state either a maximally entangled state passing through the same channel, i.e., the Choi-state, or a state that is entangled at least as much as the Choi-state. Since the construction of the Choi-state requires infinite mean energy and entanglement, i.e. it is unphysical, we derive instead every physical state able to simulate a given channel through teleportation with finite resources. Finally, we use those states to generalize a previously known error correction protocol by making it able to correct noise coming from thermal loss channels, and we also show how finite-energy resource states are able to provide tight upper bounds to the secret-key capacity of Gaussian channels. |
Thursday, March 7, 2019 2:03PM - 2:15PM |
S27.00013: Recovering noise-free quantum observables Matthew Otten, Stephen K Gray We introduce a technique for recovering noise-free observables in noisy quantum systems by combining the results of many slightly different experiments. Our approach is applicable to a variety of quantum systems but we illustrate it with applications to quantum computing and quantum sensing. The approach corresponds to repeating the same quantum evolution many times with known variations on the underlying systems' error properties, e.g. the spontaneous emission and dephasing times, T1 and T2. As opposed to standard quantum error correction methods, which have an overhead in the number of qubits, our method has only an overhead in number of evaluations, allowing the overhead to, in principle, be hidden via parallelization. We show that the effective spontaneous emission, T1, and dephasing, T2, times can be increased using this method in both simulation and experiments on an actual quantum computer. We also show how to correct more complicated entangled states and how Ramsey fringes relevant to quantum sensing can be signicantly extended in time. This work was performed at the Center for Nanoscale Materials, a U.S. Department of Energy Office of Science User Facility, and supported by the U.S. Department of Energy, Oce of Science, under Contract No. DE-AC02-06CH11357. |
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