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Journal of Physics B Atomic Molecular and Optical Physics

Non-destructive discrimination of Bell states by NMR using a single ancilla qubit

Jharana Rani Samal, Manu Gupta, Prasanta Kumar Panigrahi, Anil Kumar

Published Apr 15, 2010• 26 citations
Publisher

Abstract

Discrimination of Bell states plays an important role in a number of quantum computational protocols such as teleportation and secret sharing. However, most of the protocols dealing with Bell state discrimination in the literature either involve performing correlated measurements or destroying the entanglement of the system. Here, we demonstrate an NMR-based experimental realization of a protocol for Bell state discrimination, following a scheme proposed by Gupta et al (quant-ph/0504183v1, 23 April 2005), which does not destroy the Bell state under consideration. Using the proposed protocol, one can deterministically distinguish the Bell states, without performing a measurement using the entangled basis. State discrimination is performed through two independent measurements on one ancilla qubit, which leaves the Bell states unchanged.

DOI
10.1088/0953-4075/43/9/095508

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Discrimination of Bell states plays an important role in a number of quantum computational protocols such as teleportation and secret sharing. However, most of the protocols dealing with Bell state discrimination in the literature either involve performing correlated measurements or destroying the entanglement of the system. Here, we demonstrate an NMR-based experimental realization of a protocol for Bell state discrimination, following a scheme proposed by Gupta et al (quant-ph/0504183v1, 23 April 2005), which does not destroy the Bell state under consideration. Using the proposed protocol, one can deterministically distinguish the Bell states, without performing a measurement using the entangled basis. State discrimination is performed through two independent measurements on one ancilla qubit, which leaves the Bell states unchanged.
Abstract We propose an efficient, measurement-based quantum dialogue protocol through non-destructive discrimination (NDD) of cluster state. We use ancilla-based measurements that allow the state to be reused without destroying its entanglement. The initial state is a local unitary equivalent of the five-qubit cluster state, which significantly reduces the state components from 32 to 4, simultaneously allowing one to write its different subspaces using two different bases. The protocol utilizes single qubit unitaries from the Pauli group to encode the messages, thus preserving the stabilizer nature of the initial state throughout. We demonstrate that the proposed protocol is secure under common quantum attacks and outlining the procedure for the scalability of the scheme to transmit an n -bit message. The proposed protocol has been experimentally verified using IBM quantum backend ‘IBM-Torino’ as a proof of concept. Using the stabilizer nature of the state, we further introduce a single-qubit error correction mechanism that enhances robustness against noise without requiring any additional qubits. Further, the use of NDD allows one to reuse the quantum resources in advancing the two-way dialogue, marking the importance and novelty of the proposed scheme over preexisting methods.
Nondestructive quantum state discrimination is a fundamental primitive in distributed quantum information processing, where shared multipartite entangled resources need to be identified without being consumed. In this work, we present a scalable ancilla-assisted protocol for the strict nondestructive discrimination of nnn-qubit GHZ-class states distributed among distant parties. By employing multipartite GHZ ancillary states and local unitary interactions, we show that the computational-pattern and relative-phase information of the system GHZ state can be coherently mapped onto two ancillary registers while leaving the system state unchanged. We explicitly derive the discrimination rules for three- and four-qubit GHZ-class states and develop a systematic extension to arbitrary nnn. We further investigate the discrimination protocol in the presence of depolarizing and amplitude-damping noise in the ancillary system and obtain analytical expressions for the success probability and the corresponding critical noise thresholds. The protocol is also implemented using the IBM Qiskit platform to demonstrate its experimental feasibility and reproduce the expected ancillary measurement signatures. The proposed framework provides a scalable approach to the strict nondestructive discrimination of multipartite GHZ-class states and suggests a broader interpretation of the ancillary GHZ resources as probes of decoherence, opening a possible connection to quantum decoherence sensing in distributed quantum systems.
Remote quantum-state discrimination is a critical step for the implementation of quantum communication network and distributed quantum computation. We present a protocol for remotely implementing the unambiguous discrimination between nonorthogonal states using quantum entanglements, local operations, and classical communications. This protocol consists of a remote generalized measurement described by a positive operator valued measurement (POVM). We explicitly construct the required remote POVM. The remote POVM can be realized by performing a nonlocal controlled-rotation operation on two spatially separated qubits, one is an ancillary qubit and the other is the qubit which is encoded by two nonorthogonal states to be distinguished, and a conventional local Von Neumann orthogonal measurement on the ancilla. The particular pair of states that can be remotely and unambiguously distinguished is specified by the state of the ancilla. The probability of successful discrimination is not optimal for all admissible pairs. However, for some subset it can be very close to an optimal value in an ordinary local POVM.
A complete and deterministic Bell state measurement was realized by a simple linear optics experimental scheme which adopts two-photon polarization-momentum hyperentanglement. The scheme, which is based on the discrimination among the single photon Bell states of the hyperentangled state, requires the adoption of standard single photon detectors. The four polarization Bell states have been measured with average fidelity $F=0.889\ifmmode\pm\else\textpm\fi{}0.010$ by using the linear momentum degree of freedom as the ancilla. The feasibility of the scheme has been characterized as a function of the purity of momentum entanglement.
An ancilla-based single particle measurement scheme is illustrated for Bell state discrimination which does not lead to the collapse of the wave function.It enables the extraction of partial information, e.g., parity and phase independently, that generalizes to multi-particle entangled states of qubits, which also applied to qudits.It can be used for error correction in a quantum circuit architecture involving basic gates like Hadamard and Controlled-NOT.It helps unravel the syndrome operators and, what is more, in the multi-partite state that the individual constituents lack.
We study discrimination of mmm quantum measurements in the scenario when the unknown measurement with nnn outcomes can be used only once. We show that ancilla-assisted discrimination procedures provide a nontrivial advantage over simple (ancilla-free) schemes for perfect distinguishability and we prove that inevitably $m\ensuremath{\le}n$. We derive necessary and sufficient conditions of perfect distinguishability of general binary measurements. We show that the optimization of the discrimination of projective qubit measurements and their mixtures with white noise is equivalent to the discrimination of specific quantum states. In particular, the optimal protocol for discrimination of projective qubit measurements with fixed failure rate (exploiting maximally entangled test state) is described. While minimum-error discrimination of two projective qubit measurements can be realized without any need of entanglement, we show that discrimination of three projective qubit measurements requires a bipartite probe state. Moreover, when the measurements are not projective, the non-maximally entangled test states can outperform the maximally entangled ones. Finally, we rephrase the unambiguous discrimination of measurements as quantum key distribution protocol.