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European Quantum Electronics Conference (EQEC)

Active switching in long distance quantum state teleportation

Rainer Kaltenbaek, Rupert Ursin, Markus Aspelmeyer, Thomas D. Jennewein, Michael Lindenthal, Anton Zeilinger

Published Jan 1, 2003• 1 citation
Publisher

Abstract

Summary form only given. Quantum state teleportation is a fundamental scheme of quantum communication and computation. A full implementation of the protocol requires to actively perform a unitary transformation on the teleported quantum state, depending on the outcome of a Bell-state measurement on Alice's side. Up to now, only "passive" schemes for teleporting arbitrary qubits exist, i.e. three out of four teleportation events have to be rejected. We present a scheme where the distinction of two Bell-states is combined with an active control over the mandatory unitary transformation at Bob's side. By transmitting the entangled pair through a long fibre while broadcasting Alice's result one can achieve that the classical signal overtakes the quantum signal allowing Bob to switch before the teleported photon arrives. This is another important step towards the implementation of quantum teleportation as a tool in quantum communication schemes.

DOI
10.1109/eqec.2003.1314277

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Summary form only given. Quantum state teleportation is a fundamental scheme of quantum communication and computation. A full implementation of the protocol requires to actively perform a unitary transformation on the teleported quantum state, depending on the outcome of a Bell-state measurement on Alice's side. Up to now, only "passive" schemes for teleporting arbitrary qubits exist, i.e. three out of four teleportation events have to be rejected. We present a scheme where the distinction of two Bell-states is combined with an active control over the mandatory unitary transformation at Bob's side. By transmitting the entangled pair through a long fibre while broadcasting Alice's result one can achieve that the classical signal overtakes the quantum signal allowing Bob to switch before the teleported photon arrives. This is another important step towards the implementation of quantum teleportation as a tool in quantum communication schemes.
What is proposed here is a simple modication in the quantum protocol [1] for achieving instantaneous teleportation of arbitrary quantum state from Alice to Bob even when Bob is several light years away. This modied quantum protocol is constructed by adding a step the in the celebrated quantum teleportation protocol [1]. It consists of the action of a unitary operator to be performed by Alice on the qubits in her possession before she does the Bell basis measurement. It is important to note that the existing quantum teleportation protocol [1] requires certain classical communication between the participants, Alice and Bob, and we are going to eliminate this classical communication through our modification. In the existing protocol [1] Alice requires sending the classical bits generated during her Bell basis measurement over a classical channel to Bob for Bob to use these classical bits to determine the exact recovery operation to be performed on the qubit(s) in his possession for creating the exactly identical copy of unknown quantum state that was with Alice and got destroyed during her Bell basis measurement. Alice cannot send the classical bits she obtained to Bob with the speed faster than that of light since it is the well known experimentally veried universal upper limit on the speed. We show that by incorporating suitable unitary operation to be performed by Alice on her qubits before the Bell basis measurement the requirement of the transmission of classical bits by Alice to Bob for the creation of the unknown quantum state by Bob at his place can be completely eliminated. Our modification in the teleportation protocols [1], [2] thus clearly demonstrates the enormous advantage of remaining in the quantum regime and avoiding the requirement of any classical communication for the teleportation of the quantum states.
Summary form only given. Characterizing the entanglement of a general bipartite quantum system is a difficult problem. Most measures involve difficult extremizations and their physical motivation is not always clear. In this paper we propose an experimental measure of entanglement based on a modified version of the familiar teleportation protocol of Bennett et al. (1993). Briefly, teleportation traditionally involves two parties, Alice and Bob. Initially, Alice has a qubit in an unknown quantum state which she would like to communicate to Bob and Bob has two qubits in an entangled Einstein-Podolsky-Rosen (EPR) pair. To accomplish this transfer, Bob shares one qubit of his EPR pair with Alice. She then performs a joint measurement or Bell measurement on her two qubits and relays this information back to Bob over a classical channel. Bob then uses the outcome of Alice's Bell measurement to transform his qubit, with a local unitary transformation, into the original quantum state, always with a fidelity of one.
A scheme to teleport an unknown two qubit state from Alice (the sender) to Bob (the receiver) using two Einstein Podolsky Rosen (EPR) pairs is presented, each EPR pair being shared by both Alice and Bob. Firstly, Alice combines each of the two particles in the teleported state with an EPR particle and makes Bell state measurement on each combination. Then she transmits the outcomes of her measurements to Bob classically. According to Alice′s measurement results, Bob can perform appropriate unitary operations on his two EPR particles to retrieve the initial state.
A bidirectional quantum controlled teleportation scheme using the entanglement property of six-qubit maximally entangled state was presented.In the theoretical scheme,the sixqubit maximally entangled state was employed as the quantum channel linking three legitimate participants.Users were both sender and receiver.Alice transmitted an arbitrary single qubit state of qubit ato Bob and Bob transmitted an arbitrary single qubit state of qubit bto Alice via the control of the supervisor Charlie.Users carried out the Bell state measurements on their own particles and publicly announced their measurement results via a classical channel.Then they operated proper unitary transformation on their own particles,respectively.The bidirectional quantum controlled teleportation was successfully realized.
Quantum mechanics shows superiority than classical mechanics in many aspects and quantum entanglement plays an essential role in information processing and some computational tasks such as quantum teleportation (QT). QT was proposed to transmit the unknown states, in which EPR pairs, the entangled states, can be used as quantum channels. In this paper, we present two simple schemes for teleporting a product state of two arbitrary single-particle and an arbitrary two-particle pure entangled state respectively. Alice and Bob have shared an entangle state. Two Bell states are used as quantum channels. Then after Alice measuring her qubits and informing Bob her measurement results, Bob can perfectly reconstruct the original state by performing corresponding unitary operators on his qubits. It shown that a product state of two arbitrary single-particle and an arbitrary two-particle pure entangled state can be teleported perfectly, i.e. the success probabilities of our schemes are both 1.
In this paper, an asymmetric bidirectional controlled quantum teleportation via a six-qubit partially entangled state is given, in which Alice wants to transmit a two-qubit entangled state to Bob and Bob wants to transmit a single-qubit state to Alice on the same time. Although the six-qubit state as quantum channel is partially entangled, the teleportation is implemented deterministically. Furthermore, only Bell-state measurements, single-qubit measurements and some unitary operations are needed in the scheme.