arXiv subjects

Prasanta K. Panigrahi

Publications and source records attributed to Prasanta K. Panigrahi.

At least 145 records · Page 8Linked to original sources

arXiv2018

Quantum Locker Using a Novel Verification Algorithm and Its Experimental Realization in IBM Quantum Computer

It is well known that Grover's algorithm asymptotically transforms an equal superposition state into an eigenstate (of a given basis). Here, we demonstrate a verification algorithm based on weak measurement which can achieve the same purpose even if the qubit is not in an equal superposition state. The proposed algorithm highlights the distinguishability between any arbitrary single qubit superposition state and an eigenstate. We apply this algorithm to propose the scheme of a Quantum Locker, a protocol in which any legitimate party can verify his/her authenticity by using a newly developed quantum One-Time Password (OTP) and retrieve the necessary message from the locker. We formally explicate the working of quantum locker in association with the quantum OTP, which theoretically offers a much higher security against any adversary, as compared to any classical security device.

quant-ph↗

arXiv2018

Designing Quantum Router in IBM Quantum Computer

Quantum router is an essential ingredient in a quantum network. Here, we propose a new quantum circuit for designing quantum router by using IBM's five-qubit quantum computer. We design an equivalent quantum circuit, by the means of single-qubit and two-qubit quantum gates, which can perform the operation of a quantum router. Here, we show the routing of signal information in two different paths (two signal qubits) which is directed by a control qubit. According to the process of routing, the signal information is found to be in a coherent superposition of two paths. We demonstrate the quantum nature of the router by illustrating the entanglement between the control qubit and the two signal qubits (two paths), and confirm the well preservation of the signal information in either of the two paths after the routing process. We perform quantum state tomography to verify the generation of entanglement and preservation of information. It is found that the experimental results are obtained with good fidelity.

quant-ph↗

arXiv2018

Demonstration of Entanglement Purification and Swapping Protocol to Design Quantum Repeater in IBM Quantum Computer

Quantum communication is a secure way to transfer quantum information and to communicate with legitimate parties over distant places in a network. Although communication over a long distance has already been attained, technical problem arises due to unavoidable loss of information through the transmission channel. Quantum repeaters can extend the distance scale using entanglement swapping and purification scheme. Here we demonstrate the working of a quantum repeater by the above two processes. We use IBM's real quantum processor `ibmqx4' to create two pair of entangled qubits and design an equivalent quantum circuit which consequently swaps the entanglement between the two pairs. We then develop a novel purification protocol which enhances the degree of entanglement in a noisy channel that includes combined errors of bit-flip, phase-flip and phase-change error. We perform quantum state tomography to verify the entanglement swapping between the two pairs of qubits and working of the purification protocol.

quant-ph↗

arXiv2018

Demonstration of the Essentiality of Entanglement in a Deutsch-like Quantum Algorithm

Quantum algorithms could efficiently solve certain classically intractable problems by exploiting quantum parallelism. To date, whether the quantum entanglement is useful or not for quantum computing is still a question of debate. Here, we present a new quantum algorithm to show that entanglement could help to gain advantage over classical algorithm and even the quantum algorithm without entanglement. Furthermore, we implement experiments to demonstrate our proposed algorithm using superconducting qubits. Our results show the viability of the algorithm and suggest that entanglement is essential in getting quantum speedup for certain problems in quantum computing, which provide a reliable and clear guidance for developing useful quantum algorithms in future.

quant-ph↗

arXiv2018

Majorana zero energy modes in silicene

Zero energy modes are shown to exist in silicene under suitably chosen magnetic as well as electric fields. Two Majorana modes are found on the application of opposite local magnetization on the silicene sub-lattices. We identify a non-Majorana zero energy mode carrying pure spin current under the influence of inhomogeneous gate electric field. In both cases, wave functions reveal subtle interference pattern in phase space, showing structures finer than the Planck constant $\hbar$. A spin system coupled through spin-spin ($σ_{z}\otimesσ_{z}$) interaction with the Majorana modes exhibits periodic revival of coherence with a minimum period $\sim $1/n. The same system shows decoherence-free evolution in the case of gate electric field. Under a momentum dependent interaction, one Majorana mode having a bound state in the continuum character is found to be more robust as compared to the other. The mode arising on application of electric field shows rapid loss of coherence for such an interaction.

physics.app-ph↗

arXiv2017

Quantum secret sharing for a multipartite system under energy dissipation

We propose a protocol for multipartite secret sharing of quantum information through an \textit{amplitude damping} quantum channel. This network is, for example, of two organizations communicating with their own employees connected via classical channels locally. We consider a GHZ state distributed among four members in an asymmetric fashion where the members of a sub-party collaborate to decode the received information at their end. The target is to send two bits of information in \textit{one execution} of the protocol. Firstly, we consider an ideal channel and observe that our protocol enables decoding of a secret 2-bit information with unit probability. This is accomplished by one of the senders by the use of a globally operated \textit{quantum teleportation operator}. Secondly, we implement the same protocol in a realistic scenario under energy dissipation by the use of a parameterized \textit{amplitude damping channel} with variable noise. This noise is associated with energy dissipation and hence, loss of probability to distinguish and decode the information at the receiving end. Finally, we make this task possible through an optimization algorithm. Various channel \textit{quality measures} are also quantitatively ascertained.

quant-ph↗

arXiv2017

Light-matter interaction and Bose-Einstein condensation of light

The atom - electromagnetic field interaction is studied in the Dicke model, wherein a single field mode is interacting with a collection of two level atoms at thermal equilibrium. It is found that in the superradiant phase of the system, wherein the Bose-Einstein condensation of photons takes place, the notion of photon as an elementary electromagnetic excitation ceases to exist. The phase and intensity excitations of the condensate are found to be the true excitations of electromagnetic field. It is found that in this phase, the atom interacts with these excitations in a distinct coherent transition process, apart from the known stimulated emission/absorption and spontaneous emission processes. In the coherent transition it is found that while the atomic state changes in course of the transition process, the state of electromagnetic field remains unaffected. It is found that the transition probability of such coherent transition process is macroscopically large compared to other stimulated emission/absorption and spontaneous emission processes.

physics.optics↗

arXiv2017

Scalar-metric quantum cosmology with Chaplygin gas and perfect fluid

In this paper we consider the flat FRW cosmology with a scalar field coupled with the metric along with generalized Chaplygin gas and perfect fluid comprising the matter sector. We use the Schutz's formalism to deal with the generalized Chaplygin gas sector. The full theory is then quantized canonically using the Wheeler-DeWitt Hamiltonian formalism. We then solve the WD equation with appropriate boundary conditions. Then by defining a proper completeness relation for the self-adjointness of the WD equation we arrive at the wave packet for the universe. It is observed that the peak in the probability density gets affected due to both fluids in the matter sector, namely, the Chaplygin gas and perfect fluid.

gr-qc↗

arXiv2017

Survival of weak-field seekers inside a TOP trap

In this article, for the first time in the context of TOP trap, the necessary and sufficient conditions for the adiabatic evolution of weak field seeking states have been quantitatively examined. It has been well accepted since decades that adiabaticity has to be obeyed by the atoms for successful magnetic trapping. However, we show, on the contrary, that atoms can also be confined beyond the adiabatic limit. Hence, our findings open new possibilities to relax the restrictions of atom trapping in laboratories.

quant-ph↗

arXiv2017

Quantum Coherence and Holevo Bound

We establish the equivalence between the loss of coherence due to mixing in a quantum system and the loss of information after performing a projective measurement. Subsequently, it is demonstrated that the quantum discord, a measure of correlation for the bipartite system $ρ_{Alice\leftarrow Bob}$, is identical to the minimum difference (over all projectors {|i><i|}) between local coherence (LQICC monotone) on Bob side and coherence of the reduced density matrix $ρ^B$.

quant-ph↗

arXiv2017

The Minimum Distance of PPT Bound Entangled States from the Maximally Mixed State

Using a geometric measure of entanglement quantification based on Euclidean distance of the Hermitian matrices, we obtain the minimum distance between a bipartite bound entangled $n$- qudit density matrix and the maximally mixed state.This minimum distance for which entangled density matrices necessarily have positive partial transpose (PPT) is obtained as $\frac{1}{\sqrt{\sqrt{d^n(d^n-1)}+1}}$, which is also a lower limit for the existence of 1-distillable entangled states. The separable states necessarily lie within a minimum distance of $\frac{R}{1+d^{n-1}}$ from the Identity,where R is the radius of the closed ball homeomorphic to the set of density matrices, which is lesser than the limit for the limit for PPT bound entangled states. Furthermore an alternate proof on the non-emptiness of the PPT bound entangled states has also been given.

quant-ph↗

arXiv2017

Heun polynomials and exact solutions for the massless Dirac particle in the C-metric

The equation of motion of a massless Dirac particle in the C-metric leads to the general Heun equation (GHE) for the radial and the polar variables. The GHE, under certain parametric conditions, has been cast in terms of a new set of $su(1,1)$ generators involving differential operators of \emph{degrees} $\pm 1/2$ and $0$. Additional \emph{Heun polynomials} are obtained using this new algebraic structure and are used to construct some exact solutions for the radial and the polar parts of the Dirac equation.

gr-qc↗

arXiv2017

Quantum State Transfer through Coherent Atom-Molecule Conversion in Bose-Einstein Condensate

We demonstrate complete quantum state transfer of an atomic Bose-Einstein condensate to molecular condensate, mediated by solitonic excitations in a cigar shaped mean-field geometry. Starting with a localized solitonic atomic condensate, we show compatible gray solitonic configuration in the molecular condensate, which results in complete atom-molecule conversion. The effect of inter and intra-species interactions on the formation of molecular condensate is explicated in the presence of Raman Photoassociation. It is found that photoassociation plays a crucial role in the coherent atom-molecule conversion as well as in the soliton dynamics. The gray soliton dispersion reveals bistable behaviour, showing a re-entrant phase in a physically accessible parametric domain.

cond-mat.quant-gas↗

arXiv2017

Automated Error Correction in IBM Quantum Computer and Explicit Generalization

Experimental realization of automated error correction is demonstrated through IBM Quantum Experience for Bell and GHZ states using a measurement based approach upon ancilla qubits. The measurement automatically activates error correcting unitary operations to restore the system to its original entangled state. We illustrate the algorithm for the maximally entangled qudit case by applying appropriate Hadamard and Controlled-NOT gates.

quant-ph↗

arXiv2017

A general inseparability criterion for non-Gaussian states

We have derived a general separability criterion for a class of two mode non-Gaussian continuous variable systems, obtained earlier using PPT, violation of which provides sufficient condition for entanglement. It has been obtained by utilizing the Cauchy-Schwarz inequality and from the basic definition of separable states. This criterion coincides with the work of Agarwal and Biswas [4] which involved inequality involving higher order correlation, for testing entanglement in non-Gaussian states.

quant-ph↗

arXiv2017

Experimental realization of quantum cheque using a five-qubit quantum computer

We demonstrate the implementation of quantum cheque, proposed by Roy Moulick and Panigrahi [Quantum Inf. Process (2016) 15: 2475], using the five-qubit IBM quantum computer. Appropriate single qubit, CNOT and Fredkin gates have been implemented for the realization of the quantum cheque transaction in a quantum networked banking system. Quantum state tomography reveals the accuracy of the implementation with comparable results from the theoretical and experimental density matrices.

quant-ph↗

arXiv2017

Photon mass via current confinement

A parity invariant theory, consisting of two massive Dirac fields, defined in three dimensional space-time, with the confinement of a certain current is studied. It is found that the electromagnetic field, when coupled minimally to these Dirac fields, becomes massive owing to the current confinement. It is seen that the origin of photon mass is not due to any kind of spontaneous symmetry breaking, but only due to current confinement.

hep-th↗

arXiv2017

Duality and quantum state engineering in cavity arrays

A system of two coupled cavities with $N-1$ photons is shown to be dynamically equivalent to an array of $N$ coupled cavities containing one photon. Every transition in the two cavity system has a dual phenomenon in terms of photon transport in the cavity array. This duality is employed to arrive at the required coupling strengths and nonlinearities in the cavity array so that controlled photon transfer is possible between any two cavities. This transfer of photons between two of the cavities in the array is effected without populating the other cavities. The condition for perfect transport enables perfect state transfer between any two cavities in the array. Further, possibility of high fidelity generation of generalized NOON states in two coupled cavities, which are dual to the Bell states of the photon in the cavity array, is established.

quant-ph↗