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Concurrence Measurement for the Two-Qubit Optical and Atomic States

Lan Zhou, Yu-Bo Sheng
2015 Entropy  
In the paper, we mainly review some direct concurrence measurement protocols of the two-qubit optical or atomic system. We first introduce the concept of concurrence for a two-qubit system.  ...  Second, we explain the approaches of the concurrence measurement in both a linear and a nonlinear optical system.  ...  Measures for the Atomic State Besides the optical system, the concurrence measurement protocols for an atomic state have also been investigated.  ... 
doi:10.3390/e17064293 fatcat:3bzdp6qkknaipassw7zqnnpkk4

Dynamics of quantum correlations and linear entropy in a multi-qubit-cavity system

Alexandra Olaya-Castro, Neil F Johnson, Luis Quiroga
2004 Journal of Optics B-Quantum and Semiclassical Optics  
Specifically we investigate quantitative relations between the concurrence and linear entropy for a two-qubit mixed system, implemented as two two-level atoms interacting with a single-mode cavity field  ...  We present a theoretical study of the relationship between entanglement and entropy in multi-qubit quantum optical systems.  ...  Acknowledgments We acknowledge funding from the Clarendon Fund and ORS (AOC), DT-LINK (NFJ) and COLCIENCIAS project 1204-05-13614 (LQ).  ... 
doi:10.1088/1464-4266/6/8/016 fatcat:65odorb5dzgelnh2k7noiyjcei

Entanglement evolution for quantum trajectories

S Vogelsberger, D Spehner
2011 Journal of Physics, Conference Series  
For two qubits coupled to a common bath, the time behavior of the mean concurrence depends strongly on the initial state. One may have C(t) = C ρ(t) .  ...  Quantum Optics V, Two perfect photon counters make a click when a photon is emitted by the atom i (i = A, B) • If D i detects a photon between t and t + dt, the qubits suffer a quantum jump [occurs with  ... 
doi:10.1088/1742-6596/306/1/012029 fatcat:q4a3yxtjobbi3iwhvo42ak5fy4

Direct measurement of concurrence for atomic two-qubit pure states

G. Romero, C. E. López, F. Lastra, E. Solano, J. C. Retamal
2007 Physical Review A. Atomic, Molecular, and Optical Physics  
We propose a general scheme to measure the concurrence of an arbitrary two-qubit pure state in atomic systems.  ...  We show that it is possible to encode the concurrence in the probability of finding all atomic qubits in the ground state.  ...  The authors are grateful to T. Schätz for useful discussions.  ... 
doi:10.1103/physreva.75.032303 fatcat:icbkrg6xjra4xbajcdb3u56jmy

Heralded entanglement of arbitrary degree in remote qubits

U. Schilling, C. Thiel, E. Solano, T. Bastin, J. von Zanthier
2009 Physical Review A. Atomic, Molecular, and Optical Physics  
The degree of entanglement, as measured by the concurrence, is found to be tunable by two easily accessible experimental parameters.  ...  Incoherent scattering of photons off two remote atoms with a Lambda-level structure is used as a basic Young-type interferometer to herald long-lived entanglement of an arbitrary degree.  ...  the qubit formed by the two lower states of atom X (X = A, B).  ... 
doi:10.1103/physreva.80.022312 fatcat:xalc2sue4zed3eopqb7zqaoqz4

Probing quantum entanglement, quantum discord, classical correlation, and the quantum state without disturbing them

Zhen-ni Li, Jia-sen Jin, Chang-shui Yu
2011 Physical Review A. Atomic, Molecular, and Optical Physics  
In this paper, we present schemes for a type of one-parameter bipartite quantum states to probe the quantum entanglement, the quantum discord, the classical correlation and the quantum state based on the  ...  It is shown that our detection does not influence all these measured quantities. We also discuss how the spontaneous emission introduced by our probe atom influences our detection.  ...  Another two-level atom as a probe qubit interacts with the two optical cavity modes simultaneously. II.  ... 
doi:10.1103/physreva.83.012317 fatcat:qrmwjculcvap5k22atikh4wtoa

Proposal for direct measurement of concurrence via visibility in a cavity QED system

Sang Min Lee, Se-Wan Ji, Hai-Woong Lee, M. Suhail Zubairy
2008 Physical Review A. Atomic, Molecular, and Optical Physics  
The scheme works for any arbitrary pure initial state of the two-qubit cavity system.  ...  It is based on the cavity-QED technology using atoms as flying qubits and relies on the identity of the two-particle visibility of the atomic probability with the concurrence of the cavity system.  ...  The proposed scheme to measure the concurrence of a two-qubit cavity system. Atoms 1 and 2 are prepared in their ground state.  ... 
doi:10.1103/physreva.77.040301 fatcat:ngalmfxyvfgzrntugfwzsm4dwq

Entanglement generation in a system of two atomic quantum dots coupled to a pool of interacting bosons

Anna Posazhennikova, Reinhard Birmuske, Martin Bruderer, Wolfgang Belzig
2013 Physical Review A. Atomic, Molecular, and Optical Physics  
The tripartite system of two atomic quantum dots and a pool of bosons reduces to a qubit-qutrit-qubit realization.  ...  The bipartite setup of only one atomic quantum dot coupled to a pool of bosons turns out to be equivalent to two qubits which easily get entangled being initially in a product state.  ...  Although an entanglement measure is not unambiguously defined for a tripartite hybrid system (one qutrit and two qubits) one can calculate a concurrence [34] : C(| ) = 3 − 3 i=1 Trρ 2 i , (12) where ρ  ... 
doi:10.1103/physreva.88.042302 fatcat:w2mwnsek6nad5i2rpxaz2buodm

Position-dependent dynamics of two qubits in a leakage cavity

Jun Jing, Zhi-Guo Lü, Hong-Ru Ma, Hang Zheng
2008 Journal of Physics B: Atomic, Molecular and Optical Physics  
The position-dependent entanglement dynamics of two qubits embedded in a leakage cavity is investigated. The two qubits are initialled in Bell states and the cavity mode is taken as a standing wave.  ...  It is found that (i) the dynamics of the Bell states can be divided into two groups according to one-photon entangled states and two-photon entangled states; (ii) the entanglement life of the one-photon  ...  Acknowledgments We would like to acknowledge the support from the National Natural Science Foundation of China under grant nos. 10575068, 10474062 and 10547126, Shanghai Education Foundation for Young  ... 
doi:10.1088/0953-4075/41/13/135502 fatcat:drbnzrh2fraufeoxziysglvtri

Reversing entanglement change by a weak measurement

Qingqing Sun, M. Al-Amri, Luiz Davidovich, M. Suhail Zubairy
2010 Physical Review A. Atomic, Molecular, and Optical Physics  
The reversal procedure involves another weak measurement, preceded and followed by bit flips applied to both qubits.  ...  For the amplitudedamping case, the entanglement partially recovers under most conditions. For the weak-measurement case, the recovery of the initial entangled state is exact.  ...  State map for a single qubit The two main operations in our scheme are amplitude damping and weak measurement. Here we discuss their state maps in the single-qubit case for better understanding.  ... 
doi:10.1103/physreva.82.052323 fatcat:vciff6py55dnznw7fdxxmvveoi

Entanglement and Bell violation with phase decoherence or dissipation

J.-B. Xu, S.-B. Li
2005 European Physical Journal D : Atomic, Molecular and Optical Physics  
We adopt the concurrence to characterize the entanglement between atom and cavities or between two optical cavities in the presence of the phase decoherence.  ...  Finally, we show that even if the atom is initially prepared in a maximally mixed state, it can also entangle the two mode cavity fields.  ...  THE ENTANGLEMENT BETWEEN ATOM AND CAVITIES OR TWO OPTICAL CAVITIES In order to quantify the degree of entanglement, several measures [13] of entanglement have been introduced for both pure and mixed  ... 
doi:10.1140/epjd/e2005-00083-y fatcat:xyu4klm4lrfirgsurodgv5efea

Controlling Entanglement Dynamics by Choosing Appropriate Ratio between Cavity-Fiber Coupling and Atom-Cavity Coupling

Liao Chang-Geng, Yang Zhen-Biao, Chen Zi-Hong, Luo Cheng-Li
2010 Communications in Theoretical Physics  
The entanglement characteristics including the so-called sudden death effect between two identical two-level atoms trapped in two separate cavities connected by an optical fiber are studied.  ...  The results show that the time evolution of entanglement is sensitive not only to the degree of entanglement of the initial state but also to the ratio between cavity-fiber coupling () and atom-cavity  ...  The concurrence ( ) C ρ for the reduced density matrix ρ of a two-qubit system is defined as arranged in decreasing order.  ... 
doi:10.1088/0253-6102/54/4/17 fatcat:66xhx23lpvbzjcc7crn363w5iy

Scheme for on-resonance generation of entanglement in time-dependent asymmetric two-qubit-cavity systems

Alexandra Olaya-Castro, Neil F. Johnson, Luis Quiroga
2004 Physical Review A. Atomic, Molecular, and Optical Physics  
We present an efficient scheme for the controlled generation of pure two-qubit states possessing any desired degree of entanglement and a prescribed symmetry in two cavity QED based systems, namely, cold  ...  trapped ions and flying atoms.  ...  We investigate the dynamical evolution of the concurrence C(ρ a,a ) which measures the degree of two-qubit entanglement [10] , and the two-qubit correlation function σ + 2 σ − 1 which measures the degree  ... 
doi:10.1103/physreva.70.020301 fatcat:3dtpm2d4yzbnfme6ipi7t3w3mq

Protecting quantum entanglement from amplitude damping

Zeyang Liao, M Al-Amri, M Suhail Zubairy
2013 Journal of Physics B: Atomic, Molecular and Optical Physics  
Quantum entanglement is a critical resource for quantum information and quantum computation.  ...  As opposed to some recently studied methods, the scheme presented here does not require weak measurement in the reversal process, leading to a faster recovery of entanglement.  ...  ACKNOWLEDGMENT This work is supported by grants from the King Abdulaziz City for Science and Technology (KACST) and from the Qatar National Research Fund (QNRF) under the NPRP project 4-520-1-083.  ... 
doi:10.1088/0953-4075/46/14/145501 fatcat:vvy7prvm5zdphp6lizjazbkf7u

Quantum entanglement for two qubits in a nonstationary cavity

Oleg L. Berman, Roman Ya. Kezerashvili, Yurii E. Lozovik
2016 Physical Review A  
The quantum entanglement and the probability of the dynamical Lamb effect for two qubits caused by non-adiabatic fast change of the boundary conditions are studied.  ...  The conditional concurrence of the qubits for each fixed number of created photons in a nonstationary cavity is obtained as a measure of the dynamical quantum entanglement due to the dynamical Lamb effect  ...  It is well-known that the possible measure of quantum entanglement of two qubits is the concurrence C [21] [22] [23] , defined for the two-qubit state |Φ |Φ = a |00 + b |01 + c |10 + d |11 (19) as C(Φ  ... 
doi:10.1103/physreva.94.052308 fatcat:wx43nfa7q5htzjofkumgtnskzy
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