16 research outputs found
Comment on "Quantum Teleportation of Eight-Qubit State via Six-Qubit Cluster State"
Recently, Zhao et al., (Int. J. Theor. Phys. 57, 516-522 (2018)) have
proposed a scheme for quantum teleportation of an eight-qubit quantum state
using a six qubit cluster state. In this comment, it's shown that the quantum
resource (multi-partite entangled state used as the quantum channel) used by
Zhao et al., is excessively high and the task can be performed using any two
Bell states as the task can be reduced to the teleportation of an arbitrary two
qubit state. Further, a trivial conceptual mistake made by Zhao et al., in the
description of the quantum channel has been pointed out. It's also mentioned
that recently a trend of proposing teleportation schemes with excessively high
quantum resources has been observed and the essence of this comment is
applicable to all such proposals.Comment: It is shown that teleportation of multi qubit-states can be done
using Bell state
Experimental realization of nondestructive discrimination of Bell states using a five-qubit quantum computer
A scheme for distributed quantum measurement that allows nondestructive or
indirect Bell measurement was proposed by Gupta et al., (Int. J. Quant. Infor.
\textbf{5} (2007) 627) and subsequently realized experimentally using an
NMR-based three-qubit quantum computer by Samal et al., (J. Phys. B,
\textbf{43} (2010) 095508). In the present work, a similar experiment is
performed using the five-qubit super-conductivity-based quantum computer, which
has been recently placed in cloud by IBM Corporation. The experiment confirmed
that the Bell state can be constructed and measured in a nondestructive manner
with a reasonably high fidelity. A comparison of the outcomes of this study and
the results obtained earlier in the NMR-based experiment has also been
performed. The study indicates that to make a scalable SQUID-based computer,
errors by the gates (in the present technology) have to be reduced
considerably.Comment: 7 figures,13 pages including 1 appendi
Complete characterization of the directly implementable quantum gates used in the IBM quantum processors
Quantum process tomography of each directly implementable quantum gate used
in the IBM quantum processors is performed to compute gate error in order to
check viability of complex quantum operations in the superconductivity-based
quantum computers introduced by IBM and to compare the quality of these gates
with the corresponding gates implemented using other technologies. Quantum
process tomography (QPT) of C-NOT gates have been performed for three
configurations available in IBM QX4 processor. For all the other allowed gates
QPT have been performed for every allowed position (i.e., by placing the gates
in different qubit lines) for IBM QX4 architecture, and thus, gate fidelities
are obtained for both single-qubit and 2-qubit gates. Gate fidelities are
observed to be lower than the corresponding values obtained in the other
technologies, like NMR. Further, gate fidelities for all the single-qubit gates
are obtained for IBM QX2 architecture by placing the gates in the third qubit
line (). It's observed that the IBM QX4 architecture yields better gate
fidelity compared to IBM QX2 in all cases except the case of
gate as far as the gate fidelity corresponding to the third qubit line is
concerned. In general, the analysis performed here leads to a conclusion that a
considerable technological improvement would be inevitable to achieve the
desired scalability required for the realization of complex quantum operations.Comment: Quantum Process tomography has been done for all the gates used in
IBM QX2 and IBM QX
Design and experimental realization of an optimal scheme for teleportion of an -qubit quantum state
An explicit scheme (quantum circuit) is designed for the teleportation of an
-qubit quantum state. It is established that the proposed scheme requires an
optimal amount of quantum resources, whereas larger amount of quantum resources
has been used in a large number of recently reported teleportation schemes for
the quantum states which can be viewed as special cases of the general
-qubit state considered here. A trade off between our knowledge about the
quantum state to be teleported and the amount of quantum resources required for
the same is observed. A proof of principle experimental realization of the
proposed scheme (for a 2-qubit state) is also performed using 5-qubit
superconductivity-based IBM quantum computer. Experimental results show that
the state has been teleported with high fidelity. Relevance of the proposed
teleportation scheme has also been discussed in the context of controlled,
bidirectional, and bidirectional-controlled state teleportation.Comment: 11 pages 4 figure
Prepare-and-measure based QKD protocol under free-space losses
In this study, we have theoretically presented a prepare-and-measure-based
SARG04 protocol over free space. It has shown that the highest secret key rate
is possible even under free-space losses with a maximum tolerance of noise.Comment: 4 pages, 1 figur
Teleportation of a qubit using entangled non-orthogonal states: A comparative study
The effect of non-orthogonality of an entangled non-orthogonal state based
quantum channel is investigated in detail in the context of the teleportation
of a qubit. Specifically, average fidelity, minimum fidelity and minimum
assured fidelity (MASFI) are obtained for teleportation of a single qubit state
using all the Bell type entangled non-orthogonal states known as quasi Bell
states. Using Horodecki criterion, it is shown that the teleportation scheme
obtained by replacing the quantum channel (Bell state) of the usual
teleportation scheme by a quasi Bell state is optimal. Further, the performance
of various quasi Bell states as teleportation channel is compared in an ideal
situation (i.e., in the absence of noise) and under different noise models
(e.g., amplitude and phase damping channels). It is observed that the best
choice of the quasi Bell state depends on the amount non-orthogonality, both in
noisy and noiseless case. A specific quasi Bell state, which was found to be
maximally entangled in the ideal conditions, is shown to be less efficient as a
teleportation channel compared to other quasi Bell states in particular cases
when subjected to noisy channels. It has also been observed that usually the
value of average fidelity falls with an increase in the number of qubits
exposed to noisy channels (viz., Alice's, Bob's and to be teleported qubits),
but the converse may be observed in some particular cases.Comment: 14 pages, 4 figure
Optical designs for realization of a set of schemes for quantum cryptography
Several quantum cryptographic schemes have been proposed and realized
experimentally in the past. However, even with an advancement in quantum
technology and escalated interest in the designing of direct secure quantum
communication schemes there are not many experimental implementations of these
cryptographic schemes. In this paper, we have provided a set of optical
circuits for such quantum cryptographic schemes, which have not yet been
realized experimentally by modifying some of our theoretically proposed secure
communication schemes. Specifically, we have proposed optical designs for the
implementation of two single photon and one entangled state based controlled
quantum dialogue schemes and subsequently reduced our optical designs to yield
simpler designs for realizing other secure quantum communication tasks, i.e.,
controlled deterministic secure quantum communication, quantum dialogue,
quantum secure direct communication, quantum key agreement, and quantum key
distribution. We have further proposed an optical design for an entanglement
swapping based deterministic secure quantum communication and its controlled
counterpart.Comment: Explicit optical designs for the implementation of secure direct
quantum communication are provide