Sovik Roy

Optimal quantum communication using multiparticle partially entangled states

We propose a three-qubit partially entangled set of states as a shared resource for optimal and faithful quantum information processing. We show that our states always violate the Svetlichny inequality, which is a Bell-type inequality whose violation is a sufficient condition for the confirmation of genuine three-qubit nonlocality. Although our states can be physically realized from the generalized Greenberger-Horne-Zeilinger (GGHZ) states using a simple quantum circuit, the nonlocal properties of the set are quite different from the GGHZ states. Instead, they are similar to the maximal slice (MS) states, even though our states are not locally equivalent to the MS states. Unlike other two- and three-qubit partially entangled states, quantum teleportation using our states results in faithful transmission of information with unit probability and unit fidelity by performing only standard measurements for the sender, controller, and receiver. We further demonstrate that dense coding also leads to the deterministic transfer of a maximum number of bits from the sender to the receiver. We also introduce witness operators able to experimentally detect the family of states introduced. This work highlights the importance of both the local as well as nonlocal aspects of quantum correlations in multiqubit systems.

Study of controlled dense coding with some discrete tripartite and quadripartite states

The paper presents a detailed study of controlled dense coding scheme for different types of three and four-particle states. It consists of GHZ state, GHZ type states, maximal slice (MS), state, 4-particle GHZ state and W class of states. It is shown that GHZ-type states can be used for controlled dense coding in a probabilistic sense. We have shown relations among parameter of GHZ type state, concurrence of the shared bipartite state by two parties with respect to GHZ type and Charlies measurement angle θ. The GHZ states as a special case of MS states, depending on parameters, have also been considered here. We have seen that tripartite W state and quadripartite W state cannot be used in controlled dense coding whereas |Wn〉ABC states can be used probabilistically. Finally, we have investigated controlled dense coding scheme for tripartite qutrit states.

A revisit to non-maximally entangled mixed states: teleportation witness, noisy channel and discord

AbstractWe constructed a class of non-maximally entangled mixed states (Adhikari et al. in Quantum Inf Comput 10:0398, 2010) and extensively studied their entanglement properties and also their usefulness as teleportation channels. In this article, we have revisited our constructed state and have studied it from three different perspectives. Since every entangled state is associated with a witness operator, we have found a suitable entanglement as well as teleportation witness operator for our non-maximally entangled mixed states. We considered the noisy channel’s effects on our constructed states to see how much it affects the states’ capacities as teleportation channels. For this purpose, we have mainly focussed on amplitude damping channel. A comparative study on concurrence and quantum discord of our constructed state of Adhikari et al. (2010) has also been carried out here.

Controlled secret sharing protocol using a quantum cloning circuit

We demonstrate the possibility of controlling the success probability of a secret sharing protocol using a quantum cloning circuit. The cloning circuit is used to clone the qubits containing the encoded information and en route to the intended recipients. The success probability of the protocol depends on the cloning parameters used to clone the qubits. We also establish a relation between the concurrence of initially prepared state, entanglement of the mixed state received by the receivers after cloning scheme and the cloning parameters of cloning machine.

Operational criterion for controlled dense coding with non-trivial tripartite entangled states

In this paper, we provide an operational criterion for controlled dense coding (CDC) with a general class of three-qubit partially entangled states. A general three-qubit pure entangled state can be classified into two inequivalent classes according to their genuine tripartite entanglement. We claim that if a three-qubit state shows entanglement characteristic similar to Greenberger–Horne–Zeilinger (GHZ)-class, then such non-trivial tripartite states are useful in CDC whereas states belonging to the W-class are not useful for that. We start with a particular class of non-trivial partially entangled states belonging to the GHZ-class and show that they are effective in CDC. Then we cite several other examples of different types of tripartite entangled states to support our conjecture.

A cloned qutrit and its utility in information processing tasks

We analyze the efficacy of an output as a resource from a universal quantum cloning machine in information processing tasks such as teleportation and dense coding. For this, we have considered the

Teleportation via maximally and non-maximally entangled mixed states

3 \otimes 3

Dense coding with mixed state and steerability

3⊗3 dimensional systems. The output states are found to be NPT states for a certain range of machine parameters. Using the output state as an entangled resource, we also study the optimal fidelities of teleportation and capacities of dense coding protocols with respect to the machine parameters and make some interesting observations. Our work is motivated from the fact that the cloning output can be used as a resource in quantum information processing and adds a valuable dimension to the applications of cloning machines.