Challenges
Datasets
Workspaces
Papers
Discussions
Leaderboard
Log inSign up
Challenges
Datasets
Workspaces
Papers
Discussions
Leaderboard
Blog
Job Board
Q3AS

© 2026 Aqora Quantum S.A.S.

TermsPrivacyLegal Notice

arXiv:0711.0689 · Physical Review A

Efficient feedback controllers for continuous-time quantum error correction

Bradley A. Chase, Andrew J. Landahl, J. M. Geremia

Published Mar 5, 2008• 33 citations
arXivHTMLPDF

Abstract

We present an efficient approach to continuous-time quantum error correction that extends the low-dimensional quantum filtering methodology developed by van Handel and Mabuchi [e-print arXiv:quant-ph/0511221] to include error recovery operations in the form of real-time quantum feedback. We expect this paradigm to be useful for systems in which error recovery operations cannot be applied instantaneously. While we could not find an exact low-dimensional filter that combined both continuous syndrome measurement and a feedback Hamiltonian appropriate for error recovery, we developed an approximate reduced-dimensional model to do so. Simulations of the five-qubit code subjected to the symmetric depolarizing channel suggests that error correction based on our approximate filter performs essentially identically to correction based on an exact quantum dynamical model.

DOI
10.1103/physreva.77.032304

Related papers

Efficient feedback controllers for continuous-time quantum error correction

Andrew J. Landahl, Bradley A. Chase, J. M. Geremia

We present an efficient approach to continuous-time quantum error correction that extends the low-dimensional quantum filtering methodology developed by van Handel and Mabuchi [quantph/0511221 (2005)] to include error recovery operations in the form of real-time quantum feedback. We expect this paradigm to be useful for systems in which error recovery operations cannot be applied instantaneously. While we could not find an exact low-dimensional filter that combined both continuous syndrome measurement and a feedback Hamiltonian appropriate for error recovery, we developed an approximate reduced-dimensional model to do so. Simulations of the five-qubit code subjected to the symmetric depolarizing channel suggests that error correction based on our approximate filter performs essentially identically to correction based on an exact quantum dynamical model.

Bulletin of the American Physical Society•Mar 14, 2008•1 citation

Continuous quantum error correction as classical hybrid control

Hideo Mabuchi

The standard formulation of quantum error correction (QEC) comprises repeated cycles of error estimation and corrective intervention in the free dynamics of a qubit register. QEC can thus be seen as a form of feedback control, and it is of interest to seek a deeper understanding of the connection between the associated theories. Here we present a focused case study within this broad program, connecting continuous QEC with elements of hybrid control theory. We show that canonical methods of the latter engineering discipline, such as recursive filtering and dynamic programming approaches to solving the optimal control problem, can be applied fruitfully in the design of separated controller structures for quantum memories based on coding and continuous syndrome measurement.

New Journal of Physics•Oct 30, 2009•40 citations

Continuous-Time Quantum Error Correction via Lindblad Feedback Control — E8 Intelligence Research

Andrew Stewart Caldin

FINDING: Continuous-time quantum error correction (CTQEC) unifies noise and correction as a single Markovian open-system dynamics governed by the Lindblad master equation, enabling feedback control without discrete syndrome measurement. | MATH: dρ/dt = -i[H,ρ] + Σ_k (L_k ρ L_k† - ½{L_k†L_k, ρ}); steady-state condition: Σ_k (L_k ρ_ss L_k† - ½{L_k†L_k, ρ_ss}) = 0; code-space projection P_c with feedback Hamiltonian H_fb = Σ_a λ_a M_a (M_a = measurement operators); recovery fidelity F = Tr[P_c ρ(t)] → 1 as t→∞ under Knill-Laflamme condition P_c L_k† L_j P_c = α_kj P_c | CONNECTION: Knill-Laflamme condition defines a code subspace invariant under error operators — structurally identical to a stabilizer lattice / root-system invariant subspace; continuous weak measurement rates and feedback gains form a control manifold whose fixed points correspond to decoherence-free subspaces (DFS), which are the quantum analogue of crystallographic symmetry-protected subspaces. No direct appearance of φ Author: Andrew Stewart Caldin, Independent Researcher, UK. Part of the E8 Intelligence Research series. Platform: e8intelligence.com

•Oct 31, 2026•0 citations

Continuous quantum error correction via quantum feedback control

Charlene Ahn, Andrew C. Doherty, Andrew J. Landahl

We describe a protocol for continuously protecting unknown quantum states from decoherence that incorporates design principles from both quantum error correction and quantum feedback control. Our protocol uses continuous measurements and Hamiltonian operations, which are weaker control tools than are typically assumed for quantum error correction. We develop a cost function appropriate for unknown quantum states and use it to optimize our state-estimate feedback. Using Monte Carlo simulations, we study our protocol for the three-qubit bit-flip code in detail and demonstrate that it can improve the fidelity of quantum states beyond what is achievable using quantum error correction when the time between quantum error-correction cycles is limited.

arXiv:quant-ph/0110111•Physical Review A•Mar 14, 2002•262 citations

Measurement-based estimator scheme for continuous quantum error correction

Sangkha Borah, Bijita Sarma, Michael J. Kewming +3 more

Canonical discrete quantum error correction (DQEC) schemes use projective von Neumann measurements on stabilizers to discretize the error syndromes into a finite set, and fast unitary gates are applied to recover the corrupted information. Quantum error correction (QEC) based on continuous measurement, known as continuous quantum error correction (CQEC), in principle, can be executed faster than DQEC and can also be resource efficient. However, CQEC requires meticulous filtering of noisy continuous measurement data to reliably extract error syndromes on the basis of which errors could be detected. In this paper, we show that by constructing a measurement-based estimator (MBE) of the logical qubit to be protected, which is driven by the noisy continuous measurement currents of the stabilizers, it is possible to accurately track the errors occurring on the physical qubits in real time. We use this MBE to develop a continuous quantum error correction (MBE-CQEC) scheme that can protect the logical qubit to a high degree, surpassing the performance of DQEC, and also allows QEC to be conducted either immediately or in delayed time with instantaneous feedbacks.

arXiv:2203.13519•Physical Review Research•Sep 14, 2022•6 citations

Continuous-time Quantum Error Correction with Noise-assisted Quantum Feedback

Gerardo Cardona, Alain Sarlette, Pierre Rouchon

We address the standard quantum error correction using the three-qubit bit-flip code, yet in continuous-time. This entails rendering a target manifold of quantum states globally attractive. Previous feedback designs could feature spurious equilibria, or resort to discrete kicks pushing the system away from these equilibria to ensure global asymptotic stability. We present a new approach that consists of introducing controls driven by Brownian motions. Unlike the previous methods, the resulting closed-loop dynamics can be shown to stabilize the target manifold exponentially. We further present a reduced-order filter formulation with classical probabilities. The exponential property is important to quantify the protection induced by the closed-loop error-correction dynamics against disturbances. We study numerically the performance of this control law and of the reduced filter.

arXiv:1902.00115•IFAC-PapersOnLine•Jan 1, 2019•10 citations
We present an efficient approach to continuous-time quantum error correction that extends the low-dimensional quantum filtering methodology developed by van Handel and Mabuchi [e-print arXiv:quant-ph/0511221] to include error recovery operations in the form of real-time quantum feedback. We expect this paradigm to be useful for systems in which error recovery operations cannot be applied instantaneously. While we could not find an exact low-dimensional filter that combined both continuous syndrome measurement and a feedback Hamiltonian appropriate for error recovery, we developed an approximate reduced-dimensional model to do so. Simulations of the five-qubit code subjected to the symmetric depolarizing channel suggests that error correction based on our approximate filter performs essentially identically to correction based on an exact quantum dynamical model.
We present an efficient approach to continuous-time quantum error correction that extends the low-dimensional quantum filtering methodology developed by van Handel and Mabuchi [quantph/0511221 (2005)] to include error recovery operations in the form of real-time quantum feedback. We expect this paradigm to be useful for systems in which error recovery operations cannot be applied instantaneously. While we could not find an exact low-dimensional filter that combined both continuous syndrome measurement and a feedback Hamiltonian appropriate for error recovery, we developed an approximate reduced-dimensional model to do so. Simulations of the five-qubit code subjected to the symmetric depolarizing channel suggests that error correction based on our approximate filter performs essentially identically to correction based on an exact quantum dynamical model.
The standard formulation of quantum error correction (QEC) comprises repeated cycles of error estimation and corrective intervention in the free dynamics of a qubit register. QEC can thus be seen as a form of feedback control, and it is of interest to seek a deeper understanding of the connection between the associated theories. Here we present a focused case study within this broad program, connecting continuous QEC with elements of hybrid control theory. We show that canonical methods of the latter engineering discipline, such as recursive filtering and dynamic programming approaches to solving the optimal control problem, can be applied fruitfully in the design of separated controller structures for quantum memories based on coding and continuous syndrome measurement.
FINDING: Continuous-time quantum error correction (CTQEC) unifies noise and correction as a single Markovian open-system dynamics governed by the Lindblad master equation, enabling feedback control without discrete syndrome measurement. | MATH: dρ/dt = -i[H,ρ] + Σ_k (L_k ρ L_k† - ½{L_k†L_k, ρ}); steady-state condition: Σ_k (L_k ρ_ss L_k† - ½{L_k†L_k, ρ_ss}) = 0; code-space projection P_c with feedback Hamiltonian H_fb = Σ_a λ_a M_a (M_a = measurement operators); recovery fidelity F = Tr[P_c ρ(t)] → 1 as t→∞ under Knill-Laflamme condition P_c L_k† L_j P_c = α_kj P_c | CONNECTION: Knill-Laflamme condition defines a code subspace invariant under error operators — structurally identical to a stabilizer lattice / root-system invariant subspace; continuous weak measurement rates and feedback gains form a control manifold whose fixed points correspond to decoherence-free subspaces (DFS), which are the quantum analogue of crystallographic symmetry-protected subspaces. No direct appearance of φ Author: Andrew Stewart Caldin, Independent Researcher, UK. Part of the E8 Intelligence Research series. Platform: e8intelligence.com
We describe a protocol for continuously protecting unknown quantum states from decoherence that incorporates design principles from both quantum error correction and quantum feedback control. Our protocol uses continuous measurements and Hamiltonian operations, which are weaker control tools than are typically assumed for quantum error correction. We develop a cost function appropriate for unknown quantum states and use it to optimize our state-estimate feedback. Using Monte Carlo simulations, we study our protocol for the three-qubit bit-flip code in detail and demonstrate that it can improve the fidelity of quantum states beyond what is achievable using quantum error correction when the time between quantum error-correction cycles is limited.
Canonical discrete quantum error correction (DQEC) schemes use projective von Neumann measurements on stabilizers to discretize the error syndromes into a finite set, and fast unitary gates are applied to recover the corrupted information. Quantum error correction (QEC) based on continuous measurement, known as continuous quantum error correction (CQEC), in principle, can be executed faster than DQEC and can also be resource efficient. However, CQEC requires meticulous filtering of noisy continuous measurement data to reliably extract error syndromes on the basis of which errors could be detected. In this paper, we show that by constructing a measurement-based estimator (MBE) of the logical qubit to be protected, which is driven by the noisy continuous measurement currents of the stabilizers, it is possible to accurately track the errors occurring on the physical qubits in real time. We use this MBE to develop a continuous quantum error correction (MBE-CQEC) scheme that can protect the logical qubit to a high degree, surpassing the performance of DQEC, and also allows QEC to be conducted either immediately or in delayed time with instantaneous feedbacks.
We address the standard quantum error correction using the three-qubit bit-flip code, yet in continuous-time. This entails rendering a target manifold of quantum states globally attractive. Previous feedback designs could feature spurious equilibria, or resort to discrete kicks pushing the system away from these equilibria to ensure global asymptotic stability. We present a new approach that consists of introducing controls driven by Brownian motions. Unlike the previous methods, the resulting closed-loop dynamics can be shown to stabilize the target manifold exponentially. We further present a reduced-order filter formulation with classical probabilities. The exponential property is important to quantify the protection induced by the closed-loop error-correction dynamics against disturbances. We study numerically the performance of this control law and of the reduced filter.