01560nas a2200157 4500008004100000245005000041210005000091260001400141520111200155100001801267700001601285700001601301700002501317700002301342856003701365 2023 eng d00aBounds on Autonomous Quantum Error Correction0 aBounds on Autonomous Quantum Error Correction c8/30/20233 a

Autonomous quantum memories are a way to passively protect quantum information using engineered dissipation that creates an "always-on'' decoder. We analyze Markovian autonomous decoders that can be implemented with a wide range of qubit and bosonic error-correcting codes, and derive several upper bounds and a lower bound on the logical error rate in terms of correction and noise rates. For many-body quantum codes, we show that, to achieve error suppression comparable to active error correction, autonomous decoders generally require correction rates that grow with code size. For codes with a threshold, we show that it is possible to achieve faster-than-polynomial decay of the logical error rate with code size by using superlogarithmic scaling of the correction rate. We illustrate our results with several examples. One example is an exactly solvable global dissipative toric code model that can achieve an effective logical error rate that decreases exponentially with the linear lattice size, provided that the recovery rate grows proportionally with the linear lattice size.

1 aShtanko, Oles1 aLiu, Yu-Jie1 aLieu, Simon1 aGorshkov, Alexey, V.1 aAlbert, Victor, V. uhttps://arxiv.org/abs/2308.1623301489nas a2200133 4500008004100000245007300041210006900114260001300183520106500196100001601261700001601277700002501293856003701318 2023 eng d00aCandidate for a passively protected quantum memory in two dimensions0 aCandidate for a passively protected quantum memory in two dimens c3/2/20233 a

An interesting problem in the field of quantum error correction involves finding a physical system that hosts a ``passively protected quantum memory,'' defined as an encoded qubit coupled to an environment that naturally wants to correct errors. To date, a quantum memory stable against finite-temperature effects is only known in four spatial dimensions or higher. Here, we take a different approach to realize a stable quantum memory by relying on a driven-dissipative environment. We propose a new model, the photonic-Ising model, which appears to passively correct against both bit-flip and phase-flip errors in two dimensions: A square lattice composed of photonic ``cat qubits'' coupled via dissipative terms which tend to fix errors locally. Inspired by the presence of two distinct Z2-symmetry-broken phases, our scheme relies on Ising-like dissipators to protect against bit flips and on a driven-dissipative photonic environment to protect against phase flips. We also discuss possible ways to realize the photonic-Ising model.

1 aLieu, Simon1 aLiu, Yu-Jie1 aGorshkov, Alexey, V. uhttps://arxiv.org/abs/2205.0976701388nas a2200133 4500008004100000245006900041210006800110260001400178520096800192100001601160700001601176700002501192856003701217 2022 eng d00aCandidate for a self-correcting quantum memory in two dimensions0 aCandidate for a selfcorrecting quantum memory in two dimensions c5/19/20223 a

An interesting problem in the field of quantum error correction involves finding a physical system that hosts a "self-correcting quantum memory," defined as an encoded qubit coupled to an environment that naturally wants to correct errors. To date, a quantum memory stable against finite-temperature effects is only known in four spatial dimensions or higher. Here, we take a different approach to realize a stable quantum memory by relying on a driven-dissipative environment. We propose a new model which appears to self correct against both bit-flip and phase-flip errors in two dimensions: A square lattice composed of photonic "cat qubits" coupled via dissipative terms which tend to fix errors locally. Inspired by the presence of two distinct Z2-symmetry-broken phases, our scheme relies on Ising-like dissipators to protect against bit flips and on a driven-dissipative photonic environment to protect against phase flips. 

1 aLieu, Simon1 aLiu, Yu-Jie1 aGorshkov, Alexey, V. uhttps://arxiv.org/abs/2205.0976700508nas a2200169 4500008004100000245006400041210006300105260001400168300001200182490000800194100001600202700001800218700001800236700002200254700002500276856003700301 2022 eng d00aKramers' degeneracy for open systems in thermal equilibrium0 aKramers degeneracy for open systems in thermal equilibrium c3/10/2022 aL1211040 v1051 aLieu, Simon1 aMcGinley, Max1 aShtanko, Oles1 aCooper, Nigel, R.1 aGorshkov, Alexey, V. uhttps://arxiv.org/abs/2105.0288801670nas a2200145 4500008004100000245008900041210006900130260001500199520119300214100002001407700001601427700001901443700002501462856003701487 2021 eng d00aClustering of steady-state correlations in open systems with long-range interactions0 aClustering of steadystate correlations in open systems with long c10/28/20213 a

Lieb-Robinson bounds are powerful analytical tools for constraining the dynamic and static properties of non-relativistic quantum systems. Recently, a complete picture for closed systems that evolve unitarily in time has been achieved. In experimental systems, however, interactions with the environment cannot generally be ignored, and the extension of Lieb-Robinson bounds to dissipative systems which evolve non-unitarily in time remains an open challenge. In this work, we prove two Lieb-Robinson bounds that constrain the dynamics of open quantum systems with long-range interactions that decay as a power-law in the distance between particles. Using a combination of these Lieb-Robinson bounds and mixing bounds which arise from "reversibility" -- naturally satisfied for thermal environments -- we prove the clustering of correlations in the steady states of open quantum systems with long-range interactions. Our work provides an initial step towards constraining the steady-state entanglement structure for a broad class of experimental platforms, and we highlight several open directions regarding the application of Lieb-Robinson bounds to dissipative systems.

1 aGuo, Andrew, Y.1 aLieu, Simon1 aTran, Minh, C.1 aGorshkov, Alexey, V. uhttps://arxiv.org/abs/2110.1536801648nas a2200193 4500008004100000245006700041210006700108260001300175300001100188490000800199520108700207100001601294700001901310700002201329700001801351700002301369700002501392856003701417 2020 eng d00aSymmetry breaking and error correction in open quantum systems0 aSymmetry breaking and error correction in open quantum systems c8/6/2020 a2404050 v1253 a

Symmetry-breaking transitions are a well-understood phenomenon of closed quantum systems in quantum optics, condensed matter, and high energy physics. However, symmetry breaking in open systems is less thoroughly understood, in part due to the richer steady-state and symmetry structure that such systems possess. For the prototypical open system---a Lindbladian---a unitary symmetry can be imposed in a "weak" or a "strong" way. We characterize the possible Zn symmetry breaking transitions for both cases. In the case of Z2, a weak-symmetry-broken phase guarantees at most a classical bit steady-state structure, while a strong-symmetry-broken phase admits a partially-protected steady-state qubit. Viewing photonic cat qubits through the lens of strong-symmetry breaking, we show how to dynamically recover the logical information after any gap-preserving strong-symmetric error; such recovery becomes perfect exponentially quickly in the number of photons. Our study forges a connection between driven-dissipative phase transitions and error correctio

1 aLieu, Simon1 aBelyansky, Ron1 aYoung, Jeremy, T.1 aLundgren, Rex1 aAlbert, Victor, V.1 aGorshkov, Alexey, V. uhttps://arxiv.org/abs/2008.02816