scholarly journals The superposition invariance of unitary operators and maximally entangled state

Author(s):  
xin-wei Zha ◽  
ning Miao ◽  
xiao-yuan Yu
2021 ◽  
Vol 7 (1) ◽  
Author(s):  
Dong-Gil Im ◽  
Chung-Hyun Lee ◽  
Yosep Kim ◽  
Hyunchul Nha ◽  
M. S. Kim ◽  
...  

AbstractQuantum teleportation exemplifies how the transmission of quantum information starkly differs from that of classical information and serves as a key protocol for quantum communication and quantum computing. While an ideal teleportation protocol requires noiseless quantum channels to share a pure maximally entangled state, the reality is that shared entanglement is often severely degraded due to various decoherence mechanisms. Although the quantum noise induced by the decoherence is indeed a major obstacle to realizing a near-term quantum network or processor with a limited number of qubits, the methodologies considered thus far to address this issue are resource-intensive. Here, we demonstrate a protocol that allows optimal quantum teleportation via noisy quantum channels without additional qubit resources. By analyzing teleportation in the framework of generalized quantum measurement, we optimize the teleportation protocol for noisy quantum channels. In particular, we experimentally demonstrate that our protocol enables to teleport an unknown qubit even via a single copy of an entangled state under strong decoherence that would otherwise preclude any quantum operation. Our work provides a useful methodology for practically coping with decoherence with a limited number of qubits and paves the way for realizing noisy intermediate-scale quantum computing and quantum communication.


2003 ◽  
Vol 3 (2) ◽  
pp. 157-164
Author(s):  
H. Bechmann-Pasquinucci ◽  
N. Gisin

We present a generalized Bell inequality for two entangled quNits. On one quNit the choice is between two standard von Neumann measurements, whereas for the other quNit there are N^2 different binary measurements. These binary measurements are related to the intermediate states known from eavesdropping in quantum cryptography. The maximum violation by \sqrt{N} is reached for the maximally entangled state. Moreover, for N=2 it coincides with the familiar CHSH-inequality.


2020 ◽  
Vol 80 (2) ◽  
Author(s):  
Pingyang He ◽  
Hongwei Yu ◽  
Jiawei Hu

Abstract We study the entanglement dynamics of two static atoms coupled with a bath of fluctuating scalar fields in vacuum in the cosmic string spacetime. Three different alignments of atoms, i.e. parallel, vertical, and symmetric alignments with respect to the cosmic string are considered. We focus on how entanglement degradation and generation are influenced by the cosmic string, and find that they are crucially dependent on the atom-string distance r, the interatomic separation L, and the parameter $$\nu $$ν that characterizes the nontrivial topology of the cosmic string. For two atoms initially in a maximally entangled state, the destroyed entanglement can be revived when the atoms are aligned vertically to the string, which cannot happen in the Minkowski spacetime. When the symmetrically aligned two-atom system is initially in the antisymmetric state, the lifetime of entanglement can be significantly enhanced as $$\nu $$ν increases. For two atoms which are initially in the excited state, when the interatomic separation is large compared to the transition wavelength, entanglement generation cannot happen in the Minkowski spacetime, while it can be achieved in the cosmic string spacetime when the position of the two atoms is appropriate with respect to the cosmic string and $$\nu $$ν is large enough.


2007 ◽  
Vol 05 (05) ◽  
pp. 673-683 ◽  
Author(s):  
YU-LING LIU ◽  
ZHONG-XIAO MAN ◽  
YUN-JIE XIA

We explicitly present two schemes for quantum teleportation of an arbitrary N-qubit entangled state using, respectively, non-maximally entangled Bell states and GHZ states as the quantum channels, and generalized Bell states as the measurement basis. The scheme succeeds with unit fidelity but less than unit probability. By introducing additional qubit and unitary operations, the success probability of these two schemes can be increased.


2009 ◽  
Vol 07 (01) ◽  
pp. 395-401 ◽  
Author(s):  
SHAHPOOR MORADI

In this letter we show that in the relativistic regime, maximally entangled state of two spin-1/2 particles not only gives maximal violation of the Bell-CHSH inequality but also gives the largest violation attainable for any pairs of four spin observables that are noncommuting for both systems. Also, we extend our results to three spin-1/2 particles. We obtain the largest eigenvalue of Bell operator and show that this value is equal to the expectation value of Bell operator on GHZ state.


2014 ◽  
Vol 108 (2) ◽  
pp. 20010 ◽  
Author(s):  
S. A. Reyes ◽  
L. Morales-Molina ◽  
M. Orszag ◽  
D. Spehner

2010 ◽  
Vol 08 (07) ◽  
pp. 1111-1120 ◽  
Author(s):  
QING-YOU MENG ◽  
FU-LIN ZHANG ◽  
JING-LING CHEN

The transfer of entanglement from source particles (SPs) to target particles (TPs) via the Heisenberg interaction H = s1 ⋅ s2 has been investigated. In our research, TPs are two qubits and SPs are two qubits or qutrits. When TPs are two qubits, we find that no matter what state the TPs are initially prepared in, at the specific time t = π the quantity of entanglement of the TPs can attain 1 after interaction with the SPs which stay on the maximally entangled state. When TPs are two qutrits, the maximal quantity of entanglement of the TPs is proportional to the quantity of entanglement of the initial state of the TPs and cannot attain 1 for almost all the initial states of the TPs. Here we propose an iterated operation which can make the TPs go to the maximal entangled state.


2014 ◽  
Vol 12 (03) ◽  
pp. 1450011 ◽  
Author(s):  
Pengfei Xing ◽  
Yimin Liu ◽  
Chuanmei Xie ◽  
Xiansong Liu ◽  
Zhanjun Zhang

Two three-party schemes are put forward for sharing quantum operations on a remote qutrit with local operation and classical communication as well as shared entanglements. The first scheme uses a two-qutrit and three-qutrit non-maximally entangled states as quantum channels, while the second replaces the three-qutrit non-maximally entangled state with a two-qutrit. Both schemes are treated and compared from the four aspects of quantum and classical resource consumption, necessary-operation complexity, success probability and efficiency. It is found that the latter is overall more optimal than the former as far as a restricted set of operations is concerned. In addition, comparisons of both schemes with other four relevant ones are also made to show their two features, including degree generalization and channel-state generalization. Furthermore, some concrete discussions on both schemes are made to expose their important features of security, symmetry and experimental feasibility. Particularly, it is revealed that the success probabilities and intrinsic efficiencies in both schemes are completely determined by the shared entanglement.


2016 ◽  
Vol 14 (01) ◽  
pp. 1650003 ◽  
Author(s):  
Jiahua Wei ◽  
Hong-Yi Dai ◽  
Ming Zhang ◽  
Le Yang ◽  
Jingsong Kuang

In this paper, we put forward two novel schemes for probabilistic remote preparation of an arbitrary quantum state with the aid of appropriate local unitary operations when the sender and the receiver only have partial information of non-maximally entangled state, respectively. The concrete implementation procedures of the novel proposals are given in detail. Additionally, the physical realizations of our proposals are discussed based on the linear optics. Because of that neither the sender nor the receiver need to know fully the information of the partially entangled state, our schemes are useful to not only expand the application range of quantum entanglement, but also enlarge the research field of probabilistic remote state preparation (RSP).


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