scholarly journals Verifying Atom Entanglement Schemes by Testing Bell's Inequality

2001 ◽  
Vol 56 (1-2) ◽  
pp. 27-34
Author(s):  
Dimitris G. Angelakis ◽  
Almut Beigea ◽  
Peter L. Knight ◽  
William J. Munro ◽  
Ben Tregenn
Keyword(s):  
Photonic Crystal ◽  
High Precision ◽  
Optical Cavity ◽  
The State ◽  
Entangled States ◽  
Quantum Mechanical ◽  
Bell’S Inequality ◽  
Entangled Photons ◽  
Bell's Inequality ◽  
State Preparation

Abstract Recent experiments to test B ell's inequality using entangled photons and ions aimed at tests of basic quantum mechanical principles. Interesting results have been obtained and many loopholes could be closed. In this paper we want to point out that tests of Bell's inequality also play an important role in verifying atom entanglement schemes. We describe as an example a scheme to prepare arbitrary entangled states of N two-level atoms using a leaky optical cavity and a scheme to entangle atoms inside a photonic crystal. During the state preparation no photons are emitted, and observing a violation of B ell's inequality is the only way to test whether a scheme works with a high precision or not.

Recent results in trapped-ion quantum computing at NIST

2001 ◽  
Vol 1 (Special) ◽  
pp. 113-123
Author(s):  
D. Kielpinski ◽  
A. Ben-Kish ◽  
J. Britton ◽  
V. Meyer ◽  
M.A. Rowe ◽  
...  
Keyword(s):  
The State ◽  
Entangled State ◽  
Bell’S Inequality ◽  
Ambient Conditions ◽  
Bell's Inequality ◽  
Quantum Register ◽  
Sigma Level ◽  
Universal Quantum ◽  
Encoding Method ◽  
First Time

We review recent experiments on entanglement, Bell's inequality, and decoherence-free subspaces in a quantum register of trapped {9Be+} ions. We have demonstrated entanglement of up to four ions using the technique of Molmer and Sorensen. This method produces the state ({|\uparrow\uparrow\rangle}+{|\downarrow\downarrow\rangle})/\sqrt{2} for two ions and the state ({\downarrow}{\downarrow}{\downarrow}{\downarrow} \rangle + | {\uparrow}{\uparrow}{\uparrow}{\uparrow} \rangle)/\sqrt{2} for four ions. We generate the entanglement deterministically in each shot of the experiment. Measurements on the two-ion entangled state violates Bell's inequality at the 8\sigma level. Because of the high detector efficiency of our apparatus, this experiment closes the detector loophole for Bell's inequality measurements for the first time. This measurement is also the first violation of Bell's inequality by massive particles that does not implicitly assume results from quantum mechanics. Finally, we have demonstrated reversible encoding of an arbitrary qubit, originally contained in one ion, into a decoherence-free subspace (DFS) of two ions. The DFS-encoded qubit resists applied collective dephasing noise and retains coherence under ambient conditions 3.6 times longer than does an unencoded qubit. The encoding method, which uses single-ion gates and the two-ion entangling gate, demonstrates all the elements required for two-qubit universal quantum logic.

scholarly journals On the role of entanglement in Schrödinger’s cat paradox

Open Physics ◽  
2008 ◽  
Vol 6 (1) ◽  
Author(s):  
Stefan Rinner ◽  
Ernst Werner
Keyword(s):  
Radioactive Substance ◽  
The State ◽  
Entangled States ◽  
Quantum Mechanical ◽  
The Core ◽  
Mechanical Formalism ◽  
Quantum Mechanical Formalism ◽  
Cat States ◽  
Quantum Optical

AbstractIn this paper we re-investigate the core of Schrödinger’s “cat paradox”. We argue that one has to distinguish clearly between superpositions of macroscopic cat states |☺〉 + |☹〉 and superpositions of entangled states |☺, ↑〉 + |☹, ↓〉 which comprise both the state of the cat (☺=alive, ☹=dead) and the radioactive substance (↑=not decayed, ↓=decayed). It is shown, that in the case of the cat experiment recourse to decoherence or other mechanisms is not necessary in order to explain the absence of macroscopic superpositions. Additionally, we present modified versions of two quantum optical experiments as experimenta crucis. Applied rigorously, quantum mechanical formalism reduces the problem to a mere pseudo-paradox.

scholarly journals How Does Nature Accomplish Spooky Action at a Distance?

Quanta ◽  
2018 ◽  
Vol 7 (1) ◽  
pp. 111
Author(s):  
Mani L. Bhaumik
Keyword(s):  
Quantum Entanglement ◽  
Quantum Correlation ◽  
Quantum Nonlocality ◽  
Quantum Mechanical ◽  
Bell’S Inequality ◽  
Bell's Inequality ◽  
Nonlocal Correlations ◽  
Satisfactory Account ◽  
Nonlocal Quantum ◽  
Action At A Distance

The enigmatic nonlocal quantum correlation that was famously derided by Einstein as "spooky action at a distance" has now been experimentally demonstrated to be authentic. The quantum entanglement and nonlocal correlations emerged as inevitable consequences of John Bell's epochal paper on Bell's inequality. However, in spite of some extraordinary applications as well as attempts to explain the reason for quantum nonlocality, a satisfactory account of how Nature accomplishes this astounding phenomenon is yet to emerge. A cogent mechanism for the occurrence of this incredible event is presented in terms of a plausible quantum mechanical Einstein–Rosen bridge.Quanta 2018; 7: 111–117.

scholarly journals Nonmaximal Entanglement Can Make Joint Remote State Preparation Absolutely Secure

2013 ◽  
Vol 23 (2) ◽  
pp. 97
Author(s):  
Cao Thi Bich ◽  
Nguyen Ba An
Keyword(s):  
Quantum State ◽  
Quantum Channel ◽  
The State ◽  
Remote State Preparation ◽  
Entangled States ◽  
Joint Remote State Preparation ◽  
State Preparation ◽  
Quantum Task

Joint remote state preparation is a multiparty global quantum task in which several parties are assigned to jointly prepare a quantum state for a remote party. Although various protocols have been proposed so far, none of them are absolutely secure in the sense that the legitimate parties (the preparers plus the receiver) can by no means identify the state to be prepared even if they all collude with each other. Here we resolve this drawback by employing the quantum channel in terms of nonmaximally entangled states whose parameters are kept secret to all the participants but used to split the information in a judicious way so that not only absolute security in the above-mentioned sense is achieved but also the performance is the simplest possible.

scholarly journals DETECTING EINSTEIN–PODOLSKY–ROSEN STEERING FOR CONTINUOUS VARIABLE WAVEFUNCTIONS

2013 ◽  
Vol 11 (02) ◽  
pp. 1350019 ◽  
Author(s):  
HONG-YI SU ◽  
JING-LING CHEN ◽  
CHUNFENG WU ◽  
DONG-LING DENG ◽  
C. H. OH
Keyword(s):  
Continuous Variable ◽  
Entangled States ◽  
Sufficient Condition ◽  
Bell’S Inequality ◽  
Necessary And Sufficient Condition ◽  
Bell's Inequality ◽  
Entropic Inequality ◽  
Einstein Podolsky Rosen ◽  
Necessary And Sufficient ◽  
Epr Steering

By use of Reid's criterion and the entropic criterion, we investigate the Einstein–Podolsky–Rosen (EPR) steering for some entangled continuous variable wavefunctions. We find that some entangled states that violate Bell's inequality will not violate Reid's EPR inequality nor the entropic inequality. This implies that neither criterion gives a necessary and sufficient condition to detect the EPR steering.

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