Sujit K. Choudhary

No-flipping as a consequence of no-signalling and non-increase of entanglement under LOCC

Abstract Non-existence of universal flipper for arbitrary quantum states is a fundamental constraint on the allowed operations performed on physical systems. The largest set of qubits that can be flipped by a single machine is a great circle of the Bloch-sphere. In this Letter, we show the impossibility of universal exact-flipping operation, first by using the fact that no faster than light communication is possible and then by using the principle of “non-increase of entanglement under LOCC”. Interestingly, in both the cases, there is no violation of the two principles if and only if the set of states to be flipped, form a great circle.

Complete proof of Gisin's theorem for three qubits

Gisins theorem assures that for any pure bipartite entangled state, there is violation of the inequality of Bell and of Clauser, Horne, Shimony, and Holt, revealing its contradiction with local realistic model. Whether a similar result holds for three-qubit pure entangled states remained unresolved. We show analytically that all three-qubit pure entangled states violate a Bell-type inequality, derived on the basis of local realism, by exploiting the Hardys nonlocality argument.

Nonlocality without inequality for spin-s systems

We critically review earlier works on Hardys nonlocality argument for two spin-s systems and show that solutions previously found in this regard were restricted due to imposition of some conditions which have no role in the argument of nonlocality. We provide a compact form of the nonlocality condition for two spin-s particles, and we also extend it to n number of spin-s particles. Finally we apply a more general kind of nonlocality argument, still without an inequality, to higher-spin systems.

Ontological Models, Preparation Contextuality and Nonlocality

The ontological model framework for an operational theory has generated much interest in recent years. The debate concerning reality of quantum states has been made more precise in this framework. With the introduction of generalized notion of contextuality in this framework, it has been shown that completely mixed state of a qubit is preparation contextual. Interestingly, this new idea of preparation contextuality has been used to demonstrate nonlocality of some

Measuring higher-dimensional entanglement

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Causality, joint measurement and Tsirelson's bound

ψ-epistemic models without any use of Bell’s inequality. In particular, nonlocality of a non maximally

A NEW PROOF OF NONEXISTENCE OF PROBABILISTIC QUANTUM CLONING MACHINE

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