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Ranjana Prakash

Publications and source records attributed to Ranjana Prakash.

13 recordsLinked to original sources
arXiv2023

Condition on n-Qubit State For Getting Perfect Quantum Teleportation

It is shown that standard quantum teleportation (SQT) with multi-qubit resource result in fidelity $(2+C)/3$ where $C$ is concurrence of the resource in bipartite entanglement between qubit going to receiver and rest of the qubits. For perfect SQT, obviously, $C=1$. For a general 3-qubit resource, we find conditions for getting perfect SQT for state expressed in any basis states. Zha et al. [Mod. Phys. Lett. B 22, 2523-2528 (2008)], who studied perfect SQT using 3-qubit resource, reported conditions for perfect SQT for only those resource states which are given in the 3-qubit canonical form of Acin representation. We show that there is an alternative easily derivable representation which gives more generalized results. To illustrate the difference between the two schemes, we build an example of 3-qubit entangled state, giving perfect SQT and not included in Zha et al. results.

quant-ph↗
arXiv2022

Probabilistic Quantum Teleportation via 3-Qubit Non-Maximally Entangled GHZ State by Repeated Generalized Measurements

We propose a scheme of repeated generalized Bell state measurement (GBSM) for probabilistic quantum teleportation of single qubit state of a particle (say, 0) using 3-qubit non-maximally entangled (NME) GHZ state as a quantum channel. Alice keeps two qubits (say, 1 and 2) of the 3-qubit resource and the third qubit (say, 3) goes to Bob. Initially, Alice performs GBSM on qubits 0 and 1 which may lead to either success or failure. On obtaining success, Alice performs projective measurement on qubit 2 in the eigen basis of $σ_{x}$. Both these measurement outcomes are communicated to Bob classically, which helps him to perform a suitable unitary transformation on qubit 3 to recover the information state. On the other hand, if failure is obtained, the next attempt of GBSM is performed on qubits 0 and 2. This process of repeating GBSM on alternate pair of qubits may continue until perfect teleportation with unit fidelity is achieved. We have obtained analytical expressions for success probability up to three repetitions of GBSM. The success probability is shown to be a polynomial function of bipartite concurrence of the NME resource. The variation of success probability with the bipartite concurrence has been plotted which shows the convergence of success probability to unity with GBSM repetitions.

quant-ph↗
arXiv2021

Controlled bi-directional quantum teleportation of superposed coherent state using five qubit cluster-type entangled coherent state as a resource

We consider the problem of bi-directional controlled quantum teleportation of information encoded in phase opposite coherent state among two distant partners Alice and Bob, with the consent of controller, Charlie. We use five-mode cluster-type entangled coherent state as the quantum resource to achieve this task. The scheme uses linear optical devices such as beam splitter, phase shifters, and photon counters. We have shown that for moderately large coherent amplitude, near-perfect bi-directional controlled teleportation can be obtained in terms of the average fidelity of teleportation.

quant-ph↗
arXiv2020

High Success Perfect Transmission of 1-Qubit Information Using Purposefully Delayed Sharing of Non-Maximally Entangled 2-Qubit Resource and Repeated Generalized Bell-State Measurements ?

We propose a new scheme in which perfect transmission of 1-qubit information is achieved with high success using purposefully delayed sharing of non-maximally entangled 2-qubit resource and repeated generalized Bell-state measurements (GBSM). Alice possesses initially all qubits and she makes repeated GBSM on the pair of qubits, consisting of (1) the qubit of information state and (2) one of the two entangled resource qubits (taken alternately) until transmission with perfect fidelity is indicated. Alice then sends to Bob, the qubit not used in the last GBSM and also the result of this GBSM and Bob applies a suitable unitary transformation to replicate exactly the information state. We calculate the success probability up to 3rd repeated attempt of GBSM and plot it with concurrence of the entangled resource state. We also discuss the maximal average fidelity. Keywords: Probabilistic quantum teleportation, Non-maximally entangled state, Generalized Bell state measurement.

quant-ph↗
arXiv2020

High success standard quantum teleportation using entangled coherent state and two-level atoms in cavities

We propose here a new idea for quantum teleportation of superposed coherent state which is not only almost perfect, in principle, but also feasible experimentally. We use entangled resource $\sim |α,\fracα{\sqrt{2}}\rangle-|-α,-\fracα{\sqrt{2}}\rangle$ in contrast with the usual $\sim |α,α\rangle-|-α,-α\rangle$ (both states unnormalized). Bob receives state which is then superposition of the states $|\pm \fracα{\sqrt{2}}\rangle$ . Bob mixes these with even or odd coherent states involving superposition of states $|\pm \fracα{\sqrt{2}}\rangle$ to obtain a two-mode state which is one of $\sim |I,0\rangle \pm |0,I\rangle$, $|I\rangle$ being the information state. Bob then obtains the teleported information by using interaction of one of these modes in two cavities with resonant two-level atoms. This scheme results in average fidelity of $\simeq 0.95$ for $|α|^2 \simeq 10$, which increases with $|α|^2$ and tends to 1 asymptotically, varying as $1-\frac{π^2}{16|α|^2}+\frac{π^2(π^2+8)}{256|α|^4}$ for large values of $|α|^2$.

quant-ph↗
arXiv2019

Controlled Quantum Teleportation of Superposed Coherent State using GHZ Entangled Coherent State

Controlled quantum teleportation of superposed coherent states using GHZ entangled 3-mode coherent states is studied. Proposed scheme can be implemented experimentally using linear optical components such as a symmetric lossless beam splitter, two phase-shifters and two photon counters. Fidelity is found close to unity for appreciable mean number of photons in coherent states and is 0.99 for mean photon number equal to two.

quant-ph↗
arXiv2016

Large Polarization Squeezing in Non-Degenerate Parametric Amplification of Coherent Radiation

Polarization squeezing is shown to occur in non-degenerate parametric amplification of coherent light and the degree of squeezing at interaction time $T$ can be as large as $1-e^{-2T}$. This gives $86.4\%$ polarization squeezing for $T=1$ and $98.2\%$ for $T=2$. One simple case when this occurs is on taking initially plane polarized light having equal amplitudes in the two modes that finally has equal intensities of two circular polarizations. This suggest the experimental settings of parameters to achieve this extent of polarization squeezing in coherent light.

quant-ph↗
arXiv2016

Polarization Squeezing in Degenerate Parametric Amplification of Coherent Light

We study polarization squeezing of a light beam initially in the coherent state using the nonlinear interaction hamiltonian $ H=k\big(\hat a_{x}^{\dagger2}+{\hat a_{x}}^2\big)$. For the degree of polarization squeezing, we use a definition written in the final form by the authors and also used in earlier papers. We find that the polarization squeezing can be very high and the degree of polarization squeezing can be less than unity by a very small amount. We achieve the polarization squeezing even for very low beam intensity under some conditions involving phase angles in the polarization modes.

quant-ph↗
arXiv2016

Alteration in Non-Classicality of Light on Passing Through a Linear Polarization Beam Splitter

We observe the polarization squeezing in the mixture of a two mode squeezed vacuum and a simple coherent light through a linear polarization beam splitter. Squeezed vacuum not being squeezed in polarization, generates polarization squeezed light when superposed with coherent light. All the three Stokes parameters of the light produced on the output port of polarization beam splitter are found to be squeezed and squeezing factor also depends upon the parameters of coherent light.

physics.optics↗
arXiv2016

Simultaneous polarization squeezing in polarized N photon state and diminution on a squeezing operation

We study polarization squeezing of a pure photon number state which is obviously polarized but the mere change in the basis of polarization leads to simultaneous polarization squeezing in all the components of Stokes operator vector except those falling along or perpendicular to the direction of polarization state, is observed. We use the most general definition of polarization squeezing and discuss the experimental feasibility of the result. We also observe that a squeezing operation like non-degenerate parametric amplification of the state does not reveal simultaneous squeezing in all Stokes operator vectors and decreases in this sense.

quant-ph↗
arXiv2014

Measurement of Anomalous Moments of Creation and Annihilation Operators

We propose a scheme for measurements of anomalous moments of creation and annihilation operators requiring only one beam splitter, only one photodetector and not many measurements with phase-shift $φ$ in homodyning. This has advantageous over scheme of Shchukin and Vogel [Phys. Rev. A 72, 043808 (2005)] which requires many photodetectors, many beam splitters and a large number of measurements with phase-shift $φ$ as a Fourier transform is calculated integrating over $φ$.

physics.optics↗
arXiv2014

A Proposal for Experimental Detection of Amplitude nth-Power Squeezing

Recently, in several theoretical investigations, amplitude nth-power squeezing has been studied with $n = 2,~3,~4,~5$. In the present paper, we give a proposal for experimental detection of amplitude $n$th-power squeezing using ordinary homodyning with coherent light for arbitrary power $n$ and discuss in detail its theory. The proposed scheme requires only repeated measurements of the factorial moments of number of photons in the light obtained after homodyning, with various shifts of phase of coherent light, and involves no approximations, whatsoever. This has advantage over the method proposed by Shchukin and Vogel [Phys. Rev. A 72 (2005) 043808] in that our method requires only one beam splitter and only one photodetector, and also lesser number of repetitions of experiment with phase-shifted coherent light.

physics.optics↗