Complete Bell-state Measurement Research Articles

Deterministic Bell state measurement with a single quantum memory

Entanglements serve as a resource for any quantum information system and are deterministically generated or swapped by a joint measurement called complete Bell state measurement (BSM). The determinism arises from a quantum nondemolition measurement of two coupled qubits with the help of readout ancilla, which inevitably requires extra physical qubits. We here demonstrate a deterministic and complete BSM with only a nitrogen atom in a nitrogen-vacancy (NV) center in diamond as a quantum memory without relying on any carbon isotopes, which are the extra qubits, by exploiting electron‒nitrogen (14N) double qutrits at a zero magnetic field. The degenerate logical qubits within the subspace of qutrits on the electron and nitrogen spins are holonomically controlled by arbitrarily polarized microwave and radiofrequency pulses via zero-field-split states as the ancilla, thus enabling the complete BSM deterministically. Since the system works under an isotope-free and field-free environment, the demonstration paves the way to realize high-fidelity quantum repeaters for long-haul quantum networks and quantum interfaces for large-scale distributed quantum computers.

Complete Bell state measurement of diamond nuclear spins under a complete spatial symmetry at zero magnetic field

The symmetry of the space where a spin qubit resides plays an essential role in the manipulation of quantum entanglement, which governs the performance of quantum information systems. Application of a magnetic field, which is usually necessary for spin manipulation and readout, inevitably breaks the spatial symmetry to induce competition among quantization axes between internal and external fields, thus limiting the purity of the entanglement. If we could manipulate and readout entanglement under a zero magnetic field, we would be able to avoid the competition among quantization axes to achieve ideally high fidelity. We here demonstrate the complete Bell state measurement, which is a core element of quantum processing, of two carbon nuclear spins in the vicinity of a diamond nitrogen-vacancy center. The demonstration was made possible by holonomic entanglement manipulations based on the geometric phase with a polarized microwave under a zero magnetic field, where the quantization axis is uniquely defined by the hyperfine field. The demonstrated scheme allows high-fidelity entanglement processing even when magnetic fields cannot be applied to the integration of superconducting and spin qubits, thereby paving the way for building fault-tolerant distributed quantum computers and quantum repeater networks.

Efficient quantum secure direct communication with complete Bell‐state measurement

Quantum secure direct communication (QSDC) is a powerful technique of transmitting confidential information directly and securely based on the pre-established secure quantum channel and block transmission. Here we propose an efficient QSDC protocol using the complete Bell-state measurement (CBSM) resorting to linear optical elements and temporal-polarization hyperentanglement. In this protocol, the polarized entangled photons are utilized as the information carrier, and all the detection events of CBSM can be identified with common single-photon detectors instead of photon number resolving detectors due to the introduction of temporal degree of freedom (DOF). Moreover, since all the two-photon detection events in CBSM are effective and can be preserved with the efficiency of 100% rather than 50% in the previous QSDC, the quantum efficiency of QSDC can be doubled by encoding more messages on entangled photon pairs.

Simultaneous certification of entangled states and measurements in bounded dimensional semiquantum games

Certification of quantum systems and operations is a central task in quantum information processing. Most current schemes rely on a tomography with fully characterized devices, while this may not be met in real experiments. Device characterizations can be removed with device-independent tests, but it is technically challenging at the moment. In this paper, we investigate the problem of certifying entangled states and measurements via semiquantum games, a type of nonlocal quantum games with well characterized quantum inputs, balancing practicality and device independence. We first design a specific bounded-dimensional semiquantum game, with which any pure entangled state and Bell state measurement operators can be simultaneously certified. Afterward via a duality treatment of state and measurement, we interpret the dual form of this game as a source-independent bounded-dimensional entanglement swapping protocol and show the whole process, including any entangled projector and Bell states, can be certified with this protocol. In particular, our results do not require a complete Bell state measurement, which is beneficial for experiments and practical use.Received 11 February 2020Accepted 12 August 2020DOI:https://doi.org/10.1103/PhysRevResearch.2.033400Published by the American Physical Society under the terms of the Creative Commons Attribution 4.0 International license. Further distribution of this work must maintain attribution to the author(s) and the published article's title, journal citation, and DOI.Published by the American Physical SocietyPhysics Subject Headings (PhySH)Research AreasEntanglement detectionNonlocalityQuantum correlations in quantum informationQuantum entanglementQuantum Information

Superdense Coding over Optical Fiber Links with Complete Bell-State Measurements.

Adopting quantum communication to modern networking requires transmitting quantum information through a fiber-based infrastructure. We report the first demonstration of superdense coding over optical fiber links, taking advantage of a complete Bell-state measurement enabled by time-polarization hyperentanglement, linear optics, and common single-photon detectors. We demonstrate the highest single-qubit channel capacity to date utilizing linear optics, 1.665±0.018, and we provide a full experimental implementation of a hybrid, quantum-classical communication protocol for image transfer.

Wigner representation for polarization-momentum hyperentanglement generated in parametric down-conversion, and its application to complete Bell-state measurement

We apply the Wigner function formalism to the study of two-photon polarization-momentum hyperentanglement generated in parametric down conversion. It is shown that the consideration of a higher number of degrees of freedom is directly related to the extraction of additional uncorrelated sets of zeropoint modes at the source. We present a general expression for the description of the quantum correlations corresponding to the sixteen Bell base states, in terms of four beams whose amplitudes are correlated through the stochastic properties of the zeropoint field. A detailed analysis of the two experiments on complete Bell-state measurement included in [Walborn et al., Phys. Rev. A 68, 042313 (2003)] is made, emphasizing the role of the zeropoint field. Finally, we investigate the relationship between the zeropoint inputs at the source and the analysers, and the limits on optimal Bell-state measurement.

Arbitrarily complete Bell-state measurement using only linear optical elements

A complete Bell-state measurement is not possible using only linear-optic elements, and most schemes achieve a success rate of no more than 50%, distinguishing, for example, two of the four Bell states but returning degenerate results for the other two. It is shown here that the introduction of a pair of ancillary entangled photons improves the success rate to 75%. More generally, the addition of ${2}^{N}\ensuremath{-}2$ ancillary photons yields a linear-optic Bell-state measurement with a success rate of $1\ensuremath{-}1/{2}^{N}$.

Quantum teleportation of electrons in quantum wires with surface acoustic waves

We propose and numerically simulate a semiconductor device based on coupled quantum wires, suitable for deterministic quantum teleportation of electrons trapped in the minima of surface acoustic waves. We exploit a network of interacting semiconductor quantum wires able to provide the universal set of gates for quantum information processing with the qubit defined by the localization of a single electron in one of two coupled channels. The numerical approach is based on a time-dependent solution of the three-particle Schr\"odinger equation. First, a maximally entangled pair of electrons is obtained via Coulomb interaction between carriers in different channels. Then, a complete Bell-state measurement involving one electron from this pair and a third electron is performed. Finally, the teleported state is reconstructed by means of local one-qubit operations. The large estimated fidelity explicitly suggests that an efficient teleportation process could be reached in an experimental setup.

Generation of a displaced qubit and entangled displaced photon state via conditional measurement and their properties

We study optical schemes for generating both a displaced photon and a displaced qubit via conditional measurement. Combining one mode prepared in different microscopic states (one-mode qubit, single photon, vacuum state) and another mode in macroscopic states (coherent state, single photon added coherent state), a conditional state in the other output mode exhibits properties of a superposition of the displaced vacuum and a single photon. We propose to use the displaced qubit and entangled states composed of the displaced photon as components for quantum information processing. Basic states of such a qubit are distinguishable from each other with high fidelity. We show that the qubit reveals both microscopic and macroscopic properties. Entangled displaced states with a coherent phase as an additional degree of freedom are introduced. We show that additional degree of freedom enables to implement complete Bell state measurement of the entangled displaced photon states.

Optical Realization of Deterministic Entanglement Concentration of Polarized Photons

We propose a scheme for optical realization of deterministic entanglement concentration of polarized photons. To overcome the difficulty due to the lack of sufficiently strong interactions between photons, teleportation is employed to transfer the polarization states of two photons onto the path and polarization states of a third photon, which is made possible by the recent experimental realization of the deterministic and complete Bell state measurement. Then the required positive operator-valued measurement and further operations can be implemented deterministically by using a linear optical setup. All these are within the reach of current technology.

Dense coding by means of the displaced photon

We propose an optical scheme to perform a complete Bell-state measurement of four entangled displaced states. The principal feature of the scheme is the use of the phase of the displaced photon. The main ingredients of the scheme are the resources of single photons, coherent radiation, and optical linear elements (beam splitters, phase-shifting devices). The optical scheme works with on-off photodetectors that cannot discriminate different numbers of detected photons. This type of measurement is adjusted for dense coding and a communication rate per photon is calculated for one partial case.

QUANTUM AUTHENTICATION USING ENTANGLED STATES

A quantum authentication scheme is presented in this paper. Two parties share Einstein-Podolsky-Rosen(EPR) pairs previously as the identification token. They create auxiliary EPR pairs to interact with the identification token. Then the authentication is accomplished by a complete Bell state measurement. This scheme is proved to be secure. If no errors and eavesdroppers exist in the transmission, the identification token is unchanged after the authentication. So it can be reused.

Deterministic quantum teleportation with atoms.

Teleportation of a quantum state encompasses the complete transfer of information from one particle to another. The complete specification of the quantum state of a system generally requires an infinite amount of information, even for simple two-level systems (qubits). Moreover, the principles of quantum mechanics dictate that any measurement on a system immediately alters its state, while yielding at most one bit of information. The transfer of a state from one system to another (by performing measurements on the first and operations on the second) might therefore appear impossible. However, it has been shown that the entangling properties of quantum mechanics, in combination with classical communication, allow quantum-state teleportation to be performed. Teleportation using pairs of entangled photons has been demonstrated, but such techniques are probabilistic, requiring post-selection of measured photons. Here, we report deterministic quantum-state teleportation between a pair of trapped calcium ions. Following closely the original proposal, we create a highly entangled pair of ions and perform a complete Bell-state measurement involving one ion from this pair and a third source ion. State reconstruction conditioned on this measurement is then performed on the other half of the entangled pair. The measured fidelity is 75%, demonstrating unequivocally the quantum nature of the process.

Hyperentanglement-assisted Bell-state analysis

We propose a simple scheme for complete Bell-state measurement of photons using hyperentangled states---entangled in multiple degrees of freedom. In addition to hyperentanglement, our scheme requires only linear optics and single photon detectors, and is realizable with current technology. At the cost of additional classical communication, our Bell-state measurement can be implemented nonlocally. We discuss the possible application of these results to quantum dense coding and quantum teleportation.

Quantum teleportation with a complete Bell state measurement

By using the quantum teleportation protocol, Alice can send an unknown quantum state (e.g. the polarization of a single photon) to Bob without ever knowing about it. This paper discusses a quantum teleportation experiment in which nonlinear interactions are used for the Bell state measurement. Since the Bell state measurement is based on nonlinear interactions, all four Bell states can be distinguished. Therefore, teleportation of a polarization state can occur with certainty, in principle. Details of the theory and the experimental set-up are discussed.

Complete Bell state measurement with a solid state device

A solid state device, composed of two photon absorption crystals, rotators, and retarders, is proposed to discriminate all the four Bell states. Crystal symmetry and interference allow the absorption of a particular Bell state. The rotators and the retarders transform the other states to the state that can be detected.

Quantum Teleportation of a Polarization State with a Complete Bell State Measurement

We report a quantum teleportation experiment in which nonlinear interactions are used for the Bell state measurements. The experimental results demonstrate the working principle of irreversibly teleporting an unknown arbitrary polarization state from one system to another distant system by disassembling into and then later reconstructing from purely classical information and nonclassical EPR correlations. The distinct feature of this experiment is that all four Bell states can be distinguished in the Bell state measurement. Teleportation of a polarization state can thus occur with certainty in principle.