Qubit carriers with internal degrees of freedom in a non-factorable state (original) (raw)

Qubit transfer limited by distinguishability of carrier particles

arXiv preprint arXiv:1209.0908, 2012

Abstract: We have studied how the quality of transfer of a qubit state depends on distinguishability of internal states of the particles carrying qubits. The transfer is implemented without any direct interaction, just by a partial exchange of photons, measurement on one of them, and conditional feed-forward correction. It appears that the quality of the transfer is only influenced by the level of distinguishability of the states of unaccessible internal degrees of freedom not used for information encoding. We have ...

Carrying qubits with particles whose noninformational degrees of freedom are nonfactorable

Physical Review A, 2013

A directly measurable parameter quantifying effective indistinguishability of particles as a resource for quantum information transfer and processing is proposed. In contrast to commonly used overlap of quantum states of particles, defined only for factorable states, this measure can be generally applied to any joint state of the particles. The relevance of this generalized measure for photons produced in parametric down-conversion has been experimentally verified. The simplest linear-optical quantum-state-transfer protocol, for which this measure directly determines fidelity of the transferred state, was experimentally tested. It has been found that even if some degrees of freedom of two particles are entangled, the particles can still serve as good carriers of qubits.

QUANTUM INFORMATION TRANSFER BETWEEN TWO QUBITS: AN INTRODUCTION

This article is the beginning of a series of theoretical works of the authors and their research group to study the physical mechanism of the quantum information (QI) transfer between two qubits. As a simple example a two-spin-qubit system with the spin-spin direct coupling and without the interaction with the environment is investigated. The rate equations are exactly solved and the interpretation of the expressions of their solution as a physical mechanism of the QI transfer between two qubits is presented. This exact solution is used to study the entanglement conservation in several classes of quantum states of the system. A general method for studying arbitrary systems of two coupled spin-qubits interacting with the environment is also proposed.

Analysis of photon-mediated entanglement between distinguishable matter qubits

We theoretically evaluate establishing remote entanglement between distinguishable matter qubits through interference and detection of two emitted photons. The fidelity of the entanglement operation is analyzed as a function of the temporal-and frequency-mode matching between the photons emitted from each quantum memory. With a general analysis, we define limits on the absolute magnitudes of temporal-and frequency-mode mismatches in order to maintain entanglement fidelities greater than 99% with two-photon detection efficiencies greater than 90%. We apply our analysis to several selected systems of quantum memories. Results indicate that high fidelities may be achieved in each system using current experimental techniques, while maintaining acceptable rates of entanglement. Thus, it might be possible to use two-photon-mediated entanglement operations between distinguishable quantum memories to establish a network for quantum communication and distributed quantum computation.

Quantum state transfer between photons preloaded with quantum information

2021

Quantum mechanics provides a “disembodied” way to transfer an unknown quantum state from one quantum system to another. However, all experiments of quantum state transfer to date are limited to cases where the target quantum system contains no prior quantum information. Here we propose a scheme for transferring a quantum state to a quantum system preloaded with quantum information. By using an optical qubit-ququart entangling gate, we have experimentally demonstrated this new protocol – transferring a qubit to a photon preloaded with one qubit of quantum information. After the state transfer, the target photon contains two qubits of quantum information, one from the qubit being transferred and the other from the pre-existing qubit. Furthermore, we have also experimentally realized the inverse operation of the aforementioned quantum state transfer, which is called the partial quantum state transfer, namely transferring one qubit of quantum information from a photon preloaded with two...

High-fidelity teleportation of independent qubits

Journal of Modern Optics, 2000

Quantum teleportation is one of the essential primitives of quantum communication. We suggest that any quantum teleportation scheme can be characterized by its efficiency, i.e. how often it succeeds to teleport, its fidelity, i.e. how well the input state is reproduced at the output, and by its insensitivity to cross talk, i.e. how well it rejects an input state that is not intended to teleport. We discuss these criteria for the two teleportation experiments of independent qubits which have been performed thus far. In the first experiment (Nature 390,575 (1997)) where the qubit states were various different polarization states of photons, the fidelity of teleportation was as high as 0.80 ± 0.05 thus clearly surpassing the limit of 2/3 which can, in principle, be obtained by a direct measurement on the qubit and classical communication. This high fidelity is confirmed in our second experiment (Phys. Rev. Lett. 80, 3891 (1998)), demonstrating entanglement swapping, that is, realizing the teleportation of a qubit which itself is still entangled to another one. This experiment is the only one up to date that demonstrates the teleportation of a genuine unknown quantum state.

Quantum-information transport to multiple receivers

Physical Review A, 2006

The importance of transporting quantum information and entanglement with high fidelity cannot be overemphasized. We present a scheme based on adiabatic passage that allows for transportation of a qubit, operator measurements and entanglement, using a 1-D array of quantum sites with a single sender (Alice) and multiple receivers (Bobs). Alice need not know which Bob is the receiver, and if several Bobs try to receive the signal, they obtain a superposition state which can be used to realize two-qubit operator measurements for the generation of maximally entangled states.

Indistinguishability of Elementary Systems as a Resource for Quantum Information Processing

Physical review letters, 2018

Typical elements of quantum networks are made by identical systems, which are the basic particles constituting a resource for quantum information processing. Whether the indistinguishability due to particle identity is an exploitable quantum resource remains an open issue. Here we study independently prepared identical particles showing that, when they spatially overlap, an operational entanglement exists that can be made manifest by means of separated localized measurements. We prove this entanglement is physical in that it can be directly exploited to activate quantum information protocols, such as teleportation. These results establish that particle indistinguishability is a utilizable quantum feature and open the way to new quantum-enhanced applications.

Indistinguishability of elementary systems as resource for quantum information processing

2017

Typical elements of quantum networks are made by identical systems, which are the basic particles constituting a resource for quantum information processing. Whether the indistinguishability due to particle identity is an exploitable quantum resource remains an open issue. Here we study independently prepared identical particles showing that, when they spatially overlap, an operational entanglement exists which can be made manifest by means of separated localized measurements. We prove this entanglement is physical in that it can be directly exploited to activate quantum information protocols, such as teleportation. These results establish that particle indistinguishability is a utilizable quantum feature and open the way to new quantum-enhanced applications.

Quantum Communication without Alignment using Multiple-Qubit Single-Photon States

Physical Review Letters, 2007

We propose a scheme for encoding logical qubits in a subspace protected against collective rotations around the propagation axis using the polarization and transverse spatial degrees of freedom of single photons. This encoding allows for quantum key distribution without the need of a shared reference frame. We present methods to generate entangled states of two logical qubits using present day down-conversion sources and linear optics, and show that the application of these entangled logical states to quantum information schemes allows for alignment-free tests of Bell's inequalities, quantum dense coding and quantum teleportation.