Joint Bell-state Measurement Research Articles

Measurement-Device-Independent Verification of a Quantum Memory.

In this Letter we report an experiment that verifies an atomic-ensemble quantum memory via a measurement-device-independent scheme. A single photon generated via Rydberg blockade in one atomic ensemble is stored in another atomic ensemble via electromagnetically induced transparency. After storage for a long duration, this photon is retrieved and interfered with a second photon to perform a joint Bell-state measurement (BSM). The quantum state for each photon is chosen based on a quantum random number generator, respectively, in each run. By evaluating correlations between the random states and BSM results, we certify that our memory is genuinely entanglement preserving.

Heralded entanglement distribution between two absorptive quantum memories.

Owing to the inevitable loss in communication channels, the distance of entanglement distribution is limited to approximately 100kilometres on the ground1. Quantum repeaters can circumvent this problem by using quantum memory and entanglement swapping2. As the elementary link of a quantum repeater, the heralded distribution of two-party entanglement between two remote nodes has only been realized with built-in-type quantum memories3-9. These schemes suffer from the trade-off between multiplexing capacity and deterministic properties and hence hinder the development of efficient quantum repeaters. Quantum repeaters based on absorptive quantum memories can overcome such limitations because they separate the quantum memories and the quantum light sources. Here we present an experimental demonstration of heralded entanglement between absorptive quantum memories. We build two nodes separated by 3.5metres, each containing a polarization-entangled photon-pair source and a solid-state quantum memory with bandwidth up to 1gigahertz. A joint Bell-state measurement in the middle station heralds the successful distribution of maximally entangled states between the two quantum memories with a fidelity of 80.4±2.2per cent (±1 standard deviation). The quantum nodes and channels demonstrated here can serve as an elementary link of a quantum repeater. Moreover, the wideband absorptive quantum memories used in the nodes are compatible with deterministic entanglement sources and can simultaneously support multiplexing, which paves the way for the construction of practical solid-state quantum repeaters and high-speed quantum networks.

Entanglement swapping with autonomous polarization-entangled photon pairs from a warm atomic ensemble.

Entanglement swapping forms a key concept in the realization of scalable quantum networks and large-scale quantum communication. For the practical implementation of entanglement swapping, completely autonomous entanglement sources and a joint Bell-state measurement (BSM) between two independent photons are essential. Here, we experimentally demonstrate entanglement swapping between two independent polarization-entangled photon-pair sources obtained via spontaneous four-wave mixing (SFWM) in a Doppler-broadened atomic ensemble of ${^{87}}{\rm Rb}$87Rb atoms. From the joint BSM, we estimate the ${\rm S}$S parameter in the Clauser-Horne-Shimony-Holt (CHSH) form of Bell's inequality and confirm the violation of the Bell-CHSH inequality by ${\rm S}={2.32} \pm {0.07}$S=2.32±0.07 with 4.5 standard deviations. We believe that this work is an important step toward realizing practical scalable quantum networks.

Quantum teleportation with mutually unbiased bases

During the realization of one-qubit quantum teleportation, an EPR pair shared between two parties is required, followed by a joint Bell state measurement on the teleported qubit and the sender’s qubit. In this paper, we analyze the joint measurements in the case of teleporting multiple qubits. By carefully dividing the sender’s qubit space into several subspaces, we show that the receiver can restore the qubits if the measurement is taken in the mutually unbiased basis. We generalize our protocol to teleporting special entangled states and high-dimensional state. Our protocol may have potential application in multi-qubit quantum teleportation.

Anonymous communication scheme based on quantum walk on Cayley graph

Information security is the cornerstone and lifeblood of national security in the information society, and anonymous quantum communication is one of the important ways to protect information security. Using quantum walk randomness to effectively solve sensitive problems such as leakage of identity information. In this paper, an anonymous communication scheme based on quantum walks on the Cayley graph is proposed. First, both parties in the communication hide their identity information, and the sender Alice anonymously selects the receiver Bob through logic or operation. Secondly, the trusted third party and the communicating parties use the BB84 protocol to generate and distribute the security key. Alice encrypts the information sequence according to the security key to obtain the blind information; Bob uses the joint Bell state measurement and security key to sign and the trusted third party verifies the signature information. Third, the trusted third party calculates the position probability distribution function of Bob’s quantum walk via the Fourier transform, converts the position information corresponding to the maximum probability into a confirmation frame and sends it to Alice; Alice uses the quantum compression algorithm by decreasing dimensions to reduce the number of transmitted information bits(the length of the information bit can be reduced by up to 37.5%) and uses the security key to complete the information encryption and then transmit the information to the location indicated by the confirmation frame. Bob uses quantum walks to search the location node to obtain the transmission information and complete the anonymous quantum communication. Finally, the security analysis of the scheme is carried out, and the numerical simulation results of the Cayley graph of 200 nodes are given. At the 10-step walk, the maximal probability of the 6th node is 45.31%. According to the simulation results, the probability that Bob is eavesdropped on the specific location at his 10-step walk during the communication of this scheme is approximately 6 × 10<sup>–7</sup>%, so the receiver can avoid the identity information from the eavesdropping with a high probability, and the quantum network anonymity protocol is not broken.

Remote Preparation of a Two-ion Entangled State with a Four-ion Cluster State

The important protocol of remote preparation of an unknown two-ion entangled state with a maximally four-ion cluster state as quantum channel can be demonstrated in the ion-trap system. The two-ion entangled state can be transmitted from the sender to the receiver without apparent joint Bell-state measurement. The successful possibilities and fidelities of the scheme can reach 1.

Controlled Quantum State Transfer with Separate Measurements in Cavity QED

An experimental scheme on controlled quantum state transfer is proposed in cavity quantum electrodynamics (QED) without joint Bell-state measurement (BSM). A quantum state can be transferred perfectly with the help of the cooperation of the third side by constructing a three-atom GHZ entangled state as the controlled channel. This scheme is insensitive to the cavity decay and the thermal field. The probability of the success in our scheme is 1.0.

Concentration scheme for partially entangled photon states via entanglement reflector and no Bell-state analysis

We propose a protocol to concentrate partially entangled states of photons using entanglement reflector, which consists of a single electron spin confined in a charged quantum dot inside a single-sided microcavity. The outstanding advantage of the proposed scheme is its experimental simplicity and feasibility since it only needs to perform a single local measurement on electronic spins rather than a joint Bell-state measurement on photons. We then extend this scheme to concentrate N-photon Greenberger–Horne–Zeilinger state. Finally, we analyze the influence of various imperfections on the scheme.

Quantum Teleportation and Quantum Information Splitting by Using a Genuinely Entangled Six-Qubit State

A new application of the genuinely entangled six-qubit state introduced recently by Tapiador et al. (J. Phys. A 42:415301, 2009) is investigated for the quantum teleportation of an arbitrary three-qubit state and for quantum information splitting (QIS) of an arbitrary two-qubit state. For QIS, we have shown that it can be completed perfectly with two distinct measurement methods. In our scheme, the joint Bell-state measurement and the joint multi-qubit measurement are needed. This quantum teleportation and QIS schemes are deterministic.

Quantum Teleportation of an Unknown Two-Atom Entangled State Using Four-Atom Cluster State

A simply protocol for quantum teleportation of an unknown two-atom entangled state using four-atom cluster state is investigated in cavity quantum electrodynamics (QED). In this protocol, by using a one-dimensional maximally four-atom cluster state as quantum channel, an unknown two-atom entangled state can be transmitted from the sender (Alice) to the receiver without apparent joint Bell-state measurement. According to the results measured by the sender, the receiver can obtain the original state with unit successful probability. The important features of our scheme can also be demonstrated in ion trap system.

Three-Party Quantum Secure Sharing Using a Four-Particle Cluster State and Driven Cavity QED

We propose a scheme for implementing three-party quantum secure sharing via a four-particle cluster state in driven cavity QED. In our protocol, each of the two receivers can read out the sender’s secret communication message only if they choose to cooperate with each other. The protocol does not require the joint Bell-state measurement needed in the previous schemes and can considerably reduce the realization difficulty in experiment. Moreover, the cavity is only virtually excited and thus is insensitive to the cavity decay and the thermal field. The probability of success in our scheme can reach 1.0.

QUANTUM SECURE DIRECT COMMUNICATION WITH ONLY SEPARATE MEASUREMENTS IN DRIVEN CAVITY QED

An experimentally feasible new scheme for quantum secure direct communication is proposed in cavity quantum electrodynamics without apparent joint Bell-state measurement. The legitimate user can receive different secret messages in a direct way through Einstein–Podolsky–Rosen (EPR) pairs, the probability of the success in our scheme is unity. In the communication processes, the interactions between atoms and a single-mode non-resonant cavity with the assistance of a strong classical driving field substitute the joint measurements. Hence, this scheme needs only separate measurements. In addition, the scheme is insensitive to the cavity decay and the thermal field. The discussion of the scheme indicates that it can be realized based on current technologies.

Teleportation of a controllable orbital angular momentum generator

We report on a teleportation scheme, in which a controllable orbital angular momentum (OAM) generator is teleported. Via our scheme, Alice is able to---according to another independent photon's spin state (polarization) sent by Carol---electrically control the remote OAM generation on Bob's photon. To this end, we introduce a local electrically tunable and spin-dependent OAM generator to transfer a preliminary OAM-OAM entanglement to a spin-OAM hybrid entanglement, which then makes a joint Bell-state measurement on Alice and Carol's photons play its role. We show that the quantum state tomography can be introduced to evaluate the performance of the teleportation.

Controlled Quantum Secure Direct Communication with Local Separate Measurements in Cavity QED

In this paper, we proposed an experimentally feasible new scheme for controlled quantum secure direct communication in cavity quantum electrodynamics without apparent joint Bell-state measurement. According to the results measured by the sender and the controller, the receiver can obtain different secret messages in a deterministic way using GHZ state as the quantum channel with unit successful probability if controller cooperates with it. In the communication processes, with the assistance of a strong classical driving field, the interactions between atoms and a single-mode nonresonant cavity substitute the generalized joint Bell-basis measurements. So this scheme only need separate measurements. In addition, the scheme is insensitive to the cavity decay and the thermal field. The discussion of the scheme indicates that it is simple and realizable with present technology.

Quantum information procession with fermions based on charge detection

This paper proposes a fermionic linear optical scheme for the teleportation and entanglement concentration via entanglement swapping based on charge detection. It also proves that this method is useful in generating entangled states such as GHZ states, W states, and cluster states by using fermionic polarizing beam splitters and single spin rotations assisted by a parity check on the fermionic qubits. This scheme is nearly deterministic (i.e., with 100% successful probability) and does not need the joint Bell state measurement required in the previous schemes.

TELEPORTATION OF AN ARBITRARY AND UNKNOWN JOSEPHSON CHARGE-QUBIT ENTANGLED STATE VIA A CLUSTER STATE

An experimentally feasible scheme for teleporting an arbitrary and unknown entangled state is proposed. In this paper, we use a cluster state as the quantum channel, and we do not need any joint Bell-state measurement (BSM). Our scheme is based on Josephson charge qubits, and the successful probability and fidelity of teleportation can both reach unity. Moreover, the current scheme can be realized within the current experimental technology.

Experimental demonstration of a BDCZ quantum repeater node

Quantum communication is a method that offers efficient and secure ways for the exchange of information in a network. Large-scale quantum communication (of the order of 100 km) has been achieved; however, serious problems occur beyond this distance scale, mainly due to inevitable photon loss in the transmission channel. Quantum communication eventually fails when the probability of a dark count in the photon detectors becomes comparable to the probability that a photon is correctly detected. To overcome this problem, Briegel, Dür, Cirac and Zoller (BDCZ) introduced the concept of quantum repeaters, combining entanglement swapping and quantum memory to efficiently extend the achievable distances. Although entanglement swapping has been experimentally demonstrated, the implementation of BDCZ quantum repeaters has proved challenging owing to the difficulty of integrating a quantum memory. Here we realize entanglement swapping with storage and retrieval of light, a building block of the BDCZ quantum repeater. We follow a scheme that incorporates the strategy of BDCZ with atomic quantum memories. Two atomic ensembles, each originally entangled with a single emitted photon, are projected into an entangled state by performing a joint Bell state measurement on the two single photons after they have passed through a 300-m fibre-based communication channel. The entanglement is stored in the atomic ensembles and later verified by converting the atomic excitations into photons. Our method is intrinsically phase insensitive and establishes the essential element needed to realize quantum repeaters with stationary atomic qubits as quantum memories and flying photonic qubits as quantum messengers.

Quantum information processing for ions via linear optics

We propose a linear optical scheme for the transfer of unknown ionic states, the entanglement concentration for nonmaximally entangled states for ions via entanglement swapping and the remote preparation for ionic entangled states. The joint Bell state measurement needed in the previous schemes is not needed in the current scheme, i.e. the joint Bell state measurement has been converted into the product of separate measurements on single ions and photons. In addition, the current scheme can realize the quantum information processes for ions by using linear optical elements, which simplify the implementation of quantum information processing for ions.

Teleportation of an Unknown Atomic Entangled State Without Any Joint Bell-state Measurement via a Cluster State

An experimentally feasible scheme for teleportation of an unknown two-atom entangled state is proposed. Our scheme uses a cluster state as the quantum channel, where we do not need any joint Bell-state measurement. Moreover the successful probability and fidelity of teleportation can both reach 1.0. The current scheme can be realized within the current experimental technology.

EFFICIENT SCHEME FOR TELEPORTATION OF UNKNOWN ATOMIC STATES USING NON-MAXIMALLY ENTANGLED STATES

We propose a feasible scheme for teleporting an unknown atomic state by using non-maximally entangled states in cavity QED. The distinct advantage of the scheme is that, not only can the teleportation and distillation procedure be realized simultaneously, but the scheme is also insensitive to the cavity decay and thermal field with the assistance of a strong classical driving field. In addition, the joint Bell-state measurement can be distinguished via detecting the atomic state.