We consider an experimentally realizable scheme for manipulating quantum states using a general superposition of products of field annihilation (â) and creation (â †) operators of the type (sââ † + tâ †â), with s 2 + t 2 = 1. Such an operation, when applied on states with classical features, is shown to introduce strong nonclassicality. We quantify the generated degree of nonclassicality by the negative volume of Wigner distribution in the phase space and investigate two other observable nonclassical features, sub-Poissonian statistics and squeezing. We find that the operation introduces negativity in the Wigner distribution of an input coherent state and changes the Gaussianity of an input thermal state. This provides the possibility of engineering quantum states with specific nonclassical features. © 2012 IOP Publishing Ltd.

Rupamanjari Ghosh

SNU Management

Chatterjee A.

Dhar H.S.

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Shiv Nadar University

Journal of Physics B: Atomic, Molecular and Optical Physics

We construct a distinct class of nonlinear displaced Kerr states by application of the displacement operator upon a state which is prepared by sending the well-known photon-added coherent state through a normal Kerr medium. A sketch for the experimental setup for preparing the state is suggested. We evaluate some statistical properties such as the photon number distribution, Mandel's Q parameter, Husimi-Q and Wigner functions, and quadrature squeezing for the nonlinear displaced Kerr state and then analyze the nonclassicality in terms of these standard parameters. We reduce the infinite-level problem to a truncated discrete two-level system by using a low Kerr parameter approximation and then convert the generated nonclassicality into bipartite entanglement between the two modes of an output state of a linear optical device. © 2016 Optical Society of America.

Journal of the Optical Society of America B: Optical Physics

Nonlinear displaced Kerr state and its nonclassical properties

We investigate the states generated in continuous variable (CV) optical fields by operating them with a number-conserving operator of the type sa + ta, formed by the generalized superposition of products of field annihilation (a) and creation (a) operators, with s2 + t2 = 1. Such an operator is experimentally realizable and can be suitably manipulated to generate nonclassical optical states when applied on single- and two-mode coherent, thermal and squeezed input states. At low intensities, these nonclassical states can interact with a secondary mode via a linear optical device to generate two-mode discrete entangled states, which can serve as a resource in quantum information protocols. The advantage of these operations are tested by applying the generated entangled states as quantum channels in CV quantum teleportation, under the Braunstein and Kimble protocol. We observe that, under these operations, while the average fidelity of CV teleportation is enhanced for the nonclassical channel formed using input squeezed states, it remains at the classical threshold for input coherent and thermal states. This is due to the fact that though these operations can introduce discrete entanglement in all input states, it enhances the EinsteinPodoloskyRosen correlations only in the nonclassical squeezed state inputs, leading to an advantage in CV teleportation. This shows that nonclassical optical states generated using the above operations on classical coherent and thermal state inputs are not useful for CV teleportation. This investigation could prove useful for the efficient implementation of noisy non-Gaussian channels, formed by linear operations, in future teleportation protocols. © 2015 IOP Publishing Ltd Printed in the UK.

Generating continuous variable entangled states for quantum teleportation using a superposition of number-conserving operations

We investigate the dynamics of two-photon correlations generated by the interaction of a three-level atom in the Ξ, Λ or V configuration, with two classical external driving fields, under the rotating-wave approximation, in the presence of level decays. Using the example of a rubidium atom in each configuration, with field strengths validating the single-photon approximation, we compute measurement-based correlations, such as measurement induced disturbance (MID), quantum discord (QD), and quantum work deficit (WD), and compare the results with that from quantum entanglement (concurrence). Certain correlation properties observed are generic, model independent and consistent with known results, e.g.,MID is an upper bound on QD, QD and WD are monotonic, and the generic correlation behavior is strongly affected by the purity of the photon states. We observe that the qualitative hierarchy, monotonicity and steady-state behavior of the correlations can be controlled through the choice of parameters such as atomic decay constants and external driving field strengths. We point out how particular configurations are better suited to generating monotonic correlations in specific regimes and how the steady-state correlation behavior and hierarchy are affected by the population dynamics of the density matrix for different parameters. The possibility of using well studied quantum optical systems such as the three-level atom to generate, characterize and parametrically control mixed state quantum correlations establishes an important step in the direction of their implementation in quantum information tasks. © 2013 Elsevier Inc.

Annals of Physics

Controllable quantum correlations of two-photon states generated using classically driven three-level atoms

Reviews of Modern Physics

Gaussian quantum information

Journal of the Optical Society of America B

Nonclassicality of the photon addition-then-subtraction coherent state and its decoherence in the photon-loss channel

Physical Review A

Quantum state engineering by a coherent superposition of photon subtraction and addition

Photon-subtracted squeezed thermal state: Nonclassicality and decoherence

Nature Photonics

Entangled photons report for duty

Nonclassical properties of states engineered by superpositions of quantum operations on classical states