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

Quasi-spin wave quantum memories with dynamic symmetry $SU(2)\bar{\otimes} h_2 $

C. P. Sun, Y. Li, X. F. Liu

Published Oct 28, 2002• 0 citations
OpenAlex

Abstract

For the two-mode exciton system formed by the quasi-spin wave collective excitation of many $\\Lambda$ atoms fixed in the lattice sites of a crystal, we discover a dynamic symmetry depicted by the semi-direct product algebra $SU(2)\\bar{\\otimes} h_2 $. With the help of the spectral generating algebra method, we exactly obtain the dressed spectra of the total system formed by the two mode excitons coupling to a single mode quantized electromagnetic field in the large N limit. The exactly-obtained solutions for the eigen-states include the class of dark states extrapolating from photon to one mode quasi-spin wave exciton. These theoretical results enlighten us to propose a protocol to implement the quantum memories robust for quantum decoherence.

Related papers

Quasi-Spin-Wave Quantum Memories with a Dynamical Symmetry

C. P. Sun, Yahui Li, Xingfang Liu

For the two-mode exciton system formed by the quasi-spin-wave collective excitation of many Lambda atoms fixed at the lattice sites of a crystal, we discover a dynamical symmetry depicted by the semidirect product algebra SU2( multiply sign in circle) h(2) in the large N limit with low excitations. With the help of the spectral generating algebra method, we obtain a larger class of exact zero-eigenvalue states adiabatically interpolating between the initial state of photon-type and the final state of quasi-spin-wave exciton-type. The conditions for the adiabatic passage of dark states are shown to be valid, even with the presence of the level degeneracy. These theoretical results can lead to the proposal of a new protocol for implementing quantum memory robust against quantum decoherence.

arXiv:quant-ph/0210189•Physical Review Letters•Oct 2, 2003•142 citations

Quantum Storage Based on Collective Excitations in Atomic Ensemble

Sun Chang-Pu

In this article we reviews a new protocol of quantum memory based on the quasi-pin wave excitation of the Λ systems fixed the sites of lattice. This protocol tries to avoid the disadvantage of the quantum memory scheme based on free atom ensemble, the quantum decoherence induced by the quantum leakage of collective state. Especially, we discover a universal dynamic symmetry hidden in various ensemble based quantum storage scheme. To understand the significance of this work exactly, we also give a brief introduction to our systematical studies on collective symmetric excitons in quantum ensemble, which is the necessary to propose the present scheme for quantum memory.

Yuanzihe wuli pinglun•Jan 1, 2004•0 citations

Emergent quantum algebras in dissipative time crystals

Joseph Tindall

Strong dynamical symmetries provide an algebraic description of persistent oscillations in open quantum systems governed by the Lindblad equation. For finite-dimensional systems with a full-rank stationary state, such symmetries are necessary and sufficient for non-decaying oscillatory modes to appear in the Liouvillian's spectrum. These modes can be directly constructed by acting on stationary states with the identified symmetry operators. Here we establish an asymptotic counterpart of this algebra for collective spins. Taking a single spin $S$ in a magnetic field, subject to dissipation through linear jump operators, we identify the exact conditions on the field and dissipative couplings under which non-decaying oscillatory modes emerge as $S \rightarrow \infty$. We then write down a simple, closed form for the corresponding `symmetry' operator which can be applied to the steady state to construct these modes, which are eigenvectors of the Liouvillian, with imaginary eigenvalues, up to $O(1/S)$ corrections. A second operator, an emergent conserved quantity, completes the algebra, and its slow relaxation determines how quantum noise selects the stationary state. The construction can be directly extended to a pair of interacting spins sharing a common reservoir, with the resulting quantum algebra making the entanglement during a quench analytically accessible.

quant-pharXiv:2610.16609•Oct 13, 2026•0 citations

Decoherence in collective quantum memories for photons

Claudia K. A. Mewes, Michael Fleischhauer

The influence of decoherence on quantum memories for photons based on atomic ensembles is discussed. It is shown that despite the large entanglement of the collective storage states, corresponding to single photons or nonclassical states of light, the sensitivity to decoherence does not scale with the number of atoms. This is due to the existence of equivalence classes of storage states, which have the same projection onto the relevant quasiparticle mode (dark-state polariton). Several decoherence processes resulting from uncorrelated individual reservoir couplings are analyzed in detail: single-atom spin flips and dephasing, atom loss, and motion of atoms. Furthermore, it is shown that the sensitivity to collective decoherence processes that affect all polariton modes with comparable strength does also not increase with the number of atoms.

arXiv:quant-ph/0408018•Physical Review A•Aug 18, 2005•33 citations

Transient dynamics of light propagation in EIT medium and hidden symmetry of multi-bit quantum memory

Y. Li, Xulin Liu, Che Sun

We investigate the transient phenomenon or property of the propagation of an optical probe field in a medium consisting of many $Λ$-type three-level atoms coupled to this probe field and an classical driven field. We observe a hidden symmetry and obtain an exact solution for this light propagation problem by means of the spectral generating method. This solution enlightens us to propose a practical protocol implementing the quantum memory robust for quantum decoherence in a crystal. As an transient dynamic process this solution also manifests an exotic result that a wave-packet of light will split into three packets propagating at different group velocities. It is argued that "super-luminal group velocity" and "sub-luminal group velocity" can be observed simultaneously in the same system. This interesting phenomenon is expected to be demonstrated experimentally.

arXiv:quant-ph/0306170•Jun 25, 2003•0 citations

SU(2)×SU(2) QUASI-SPIN MODEL AND METHODS FOR RESTORING BROKEN SYMMETRIES OF SELF-CONSISTENT SOLUTIONS(I)——AN EXACT SOLUTION AND HF APPROXIMATION

Jiali Liao

A quasi-spin model containing two kinds of interactions is proposed. Tbe exact solutionsof the model Hamiltonian on SU(2)×SU(2) basis, the ground-state phase transition and theK-structure of the wave functions are discussed. The effectivity of HF approximation isalso studied in this model.

Science China Mathematics•Jan 1, 1991•0 citations
For the two-mode exciton system formed by the quasi-spin wave collective excitation of many Lambda\\LambdaLambda atoms fixed in the lattice sites of a crystal, we discover a dynamic symmetry depicted by the semi-direct product algebra SU(2)barotimesh2SU(2)\\bar{\\otimes} h_2 SU(2)barotimesh2​. With the help of the spectral generating algebra method, we exactly obtain the dressed spectra of the total system formed by the two mode excitons coupling to a single mode quantized electromagnetic field in the large N limit. The exactly-obtained solutions for the eigen-states include the class of dark states extrapolating from photon to one mode quasi-spin wave exciton. These theoretical results enlighten us to propose a protocol to implement the quantum memories robust for quantum decoherence.
For the two-mode exciton system formed by the quasi-spin-wave collective excitation of many Lambda atoms fixed at the lattice sites of a crystal, we discover a dynamical symmetry depicted by the semidirect product algebra SU2( multiply sign in circle) h(2) in the large N limit with low excitations. With the help of the spectral generating algebra method, we obtain a larger class of exact zero-eigenvalue states adiabatically interpolating between the initial state of photon-type and the final state of quasi-spin-wave exciton-type. The conditions for the adiabatic passage of dark states are shown to be valid, even with the presence of the level degeneracy. These theoretical results can lead to the proposal of a new protocol for implementing quantum memory robust against quantum decoherence.
In this article we reviews a new protocol of quantum memory based on the quasi-pin wave excitation of the Λ systems fixed the sites of lattice. This protocol tries to avoid the disadvantage of the quantum memory scheme based on free atom ensemble, the quantum decoherence induced by the quantum leakage of collective state. Especially, we discover a universal dynamic symmetry hidden in various ensemble based quantum storage scheme. To understand the significance of this work exactly, we also give a brief introduction to our systematical studies on collective symmetric excitons in quantum ensemble, which is the necessary to propose the present scheme for quantum memory.
Strong dynamical symmetries provide an algebraic description of persistent oscillations in open quantum systems governed by the Lindblad equation. For finite-dimensional systems with a full-rank stationary state, such symmetries are necessary and sufficient for non-decaying oscillatory modes to appear in the Liouvillian's spectrum. These modes can be directly constructed by acting on stationary states with the identified symmetry operators. Here we establish an asymptotic counterpart of this algebra for collective spins. Taking a single spin SSS in a magnetic field, subject to dissipation through linear jump operators, we identify the exact conditions on the field and dissipative couplings under which non-decaying oscillatory modes emerge as S→∞S \rightarrow \inftyS→∞. We then write down a simple, closed form for the corresponding `symmetry' operator which can be applied to the steady state to construct these modes, which are eigenvectors of the Liouvillian, with imaginary eigenvalues, up to O(1/S)O(1/S)O(1/S) corrections. A second operator, an emergent conserved quantity, completes the algebra, and its slow relaxation determines how quantum noise selects the stationary state. The construction can be directly extended to a pair of interacting spins sharing a common reservoir, with the resulting quantum algebra making the entanglement during a quench analytically accessible.
The influence of decoherence on quantum memories for photons based on atomic ensembles is discussed. It is shown that despite the large entanglement of the collective storage states, corresponding to single photons or nonclassical states of light, the sensitivity to decoherence does not scale with the number of atoms. This is due to the existence of equivalence classes of storage states, which have the same projection onto the relevant quasiparticle mode (dark-state polariton). Several decoherence processes resulting from uncorrelated individual reservoir couplings are analyzed in detail: single-atom spin flips and dephasing, atom loss, and motion of atoms. Furthermore, it is shown that the sensitivity to collective decoherence processes that affect all polariton modes with comparable strength does also not increase with the number of atoms.
We investigate the transient phenomenon or property of the propagation of an optical probe field in a medium consisting of many ΛΛΛ-type three-level atoms coupled to this probe field and an classical driven field. We observe a hidden symmetry and obtain an exact solution for this light propagation problem by means of the spectral generating method. This solution enlightens us to propose a practical protocol implementing the quantum memory robust for quantum decoherence in a crystal. As an transient dynamic process this solution also manifests an exotic result that a wave-packet of light will split into three packets propagating at different group velocities. It is argued that "super-luminal group velocity" and "sub-luminal group velocity" can be observed simultaneously in the same system. This interesting phenomenon is expected to be demonstrated experimentally.