scholarly journals Metastable decoherence-free subspace and pointer states in mesoscopic quantum systems

2018 ◽  
Vol 97 (4) ◽  
Author(s):  
F. Lastra ◽  
C. E. López ◽  
J. C. Retamal
Keyword(s):  
Quantum Systems ◽  
Pointer States ◽  
Decoherence Free Subspace

Lyapunov control on quantum systems

2014 ◽  
Vol 28 (30) ◽  
pp. 1430020 ◽  
Author(s):  
L. C. Wang ◽  
X. X. Yi
Keyword(s):  
Quantum System ◽  
Open Quantum System ◽  
Open Quantum Systems ◽  
Logic Gates ◽  
Quantum Systems ◽  
Open Quantum ◽  
Quantum Operations ◽  
Lyapunov Control ◽  
Decoherence Free Subspace ◽  
General Method

We review the scheme of quantum Lyapunov control and its applications into quantum systems. After a brief review on the general method of quantum Lyapunov control in closed and open quantum systems, we apply it into controlling quantum states and quantum operations. The control of a spin-1/2 quantum system, driving an open quantum system into its decoherence free subspace (DFS), constructing single qubit and two-qubit logic gates are taken to illustrate the scheme. The optimalization of the Lyapunov control is also reviewed in this article.

Common reducing unitary subspaces and decoherence in quantum systems

2015 ◽  
Vol 30 ◽  
Author(s):  
Grzegorz Pastuszak ◽  
Andrzej Jamiołkowski
Keyword(s):  
Invariant Subspaces ◽  
Quantum Information Theory ◽  
Quantum Systems ◽  
Quantum Channels ◽  
Effective Condition ◽  
Arbitrary Dimensions ◽  
Fixed Complex ◽  
Definition Of ◽  
Dimension One ◽  
Decoherence Free Subspace

Maps of the form Phi(X) =sum_{i=1}^s A_iXA^*, where A_1, . . . ,A_s are fixed complex n by n matrices and X is any complex n by n matrix are used in quantum information theory as representations of quantum channels. This article deals with computable conditions for the existence of decoherence--free subspaces for Phi. Since the definition of decoherence-free subspace for quantum channels relies only on the matrices A1, . . . ,As, the term of common reducing unitary subspace is used instead of the original one. Among the main results of the paper, there are computable conditions for the existence of common eigenvectors. These are related to common reducing unitary subspaces of dimension one. The new results on common eigenvectors provide new effective condition for the existence of common invariant subspaces of arbitrary dimensions.

scholarly journals Reference Frame Induced Symmetry Breaking on Holographic Screens

Symmetry ◽  
2021 ◽  
Vol 13 (3) ◽  
pp. 408
Author(s):  
Chris Fields ◽  
James F. Glazebrook ◽  
Antonino Marcianò
Keyword(s):  
Symmetry Breaking ◽  
Reference Frame ◽  
Reference Frames ◽  
A Priori ◽  
Quantum Systems ◽  
Classical Information ◽  
Pointer States ◽  
Finite Quantum Systems ◽  
Holographic Screen ◽  
Holographic Screens

Any interaction between finite quantum systems in a separable joint state can be viewed as encoding classical information on an induced holographic screen. Here we show that when such an interaction is represented as a measurement, the quantum reference frames (QRFs) deployed to identify systems and pick out their pointer states induce decoherence, breaking the symmetry of the holographic encoding in an observer-relative way. Observable entanglement, contextuality, and classical memory are, in this representation, logical and temporal relations between QRFs. Sharing entanglement as a resource requires a priori shared QRFs.

FAULT-TOLERATE QUANTUM KEY DISTRIBUTION OVER A COLLECTIVE-NOISE CHANNEL

2010 ◽  
Vol 08 (07) ◽  
pp. 1101-1109 ◽  
Author(s):  
CHUN-YAN LI ◽  
YAN-SONG LI
Keyword(s):  
Quantum Key Distribution ◽  
Single Photon ◽  
Bell State ◽  
Key Distribution ◽  
Quantum Systems ◽  
Collective Noise ◽  
Two Photon ◽  
Intrinsic Efficiency ◽  
Decoherence Free Subspace ◽  
Bell State Measurements

We present two quantum key distribution (QKD) schemes over a collective-noise channel. Each logical qubit, composed of two physical qubits with a decoherence-free subspace, is immune to a collective noise and can carry one bit of information in theory. Although the receiver should prepare entangled two-photon quantum systems, he can read out the information encoded by the sender with two unitary operations on two photons, resorting to only two single-photon measurements, not Bell-state measurements, which makes these protocols simpler than others in experiment. These two QKD protocols are deterministic, not random, which makes the classical information exchanged be reduced largely. Also, they have a high intrinsic efficiency.

Coherent population trapping in quantum systems

1993 ◽  
Vol 163 (9) ◽  
pp. 1 ◽  
Author(s):  
B.D. Agap'ev ◽  
M.B. Gornyi ◽  
B.G. Matisov ◽  
Yu.V. Rozhdestvenskii
Keyword(s):  
Quantum Systems ◽  
Coherent Population Trapping ◽  
Population Trapping

Relaxation of interacting open quantum systems

2018 ◽  
Vol 189 (05) ◽  
Author(s):  
Vladislav Yu. Shishkov ◽  
Evgenii S. Andrianov ◽  
Aleksandr A. Pukhov ◽  
Aleksei P. Vinogradov ◽  
A.A. Lisyansky
Keyword(s):  
Open Quantum Systems ◽  
Quantum Systems ◽  
Open Quantum

Entanglement

2017 ◽  
Author(s):  
Richard Healey
Keyword(s):  
Quantum Theory ◽  
Quantum State ◽  
Physical Condition ◽  
Physical System ◽  
Polarization State ◽  
Quantum Systems ◽  
Ghz State ◽  
Mathematical Representation ◽  
Entangled State ◽  
Physical Relation

Often a pair of quantum systems may be represented mathematically (by a vector) in a way each system alone cannot: the mathematical representation of the pair is said to be non-separable: Schrödinger called this feature of quantum theory entanglement. It would reflect a physical relation between a pair of systems only if a system’s mathematical representation were to describe its physical condition. Einstein and colleagues used an entangled state to argue that its quantum state does not completely describe the physical condition of a system to which it is assigned. A single physical system may be assigned a non-separable quantum state, as may a large number of systems, including electrons, photons, and ions. The GHZ state is an example of an entangled polarization state that may be assigned to three photons.

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