Complete hyperentangled-Bell-state analysis for photonic qubits assisted by a three-level Λ-type system.

Tie-Jun Wang,Chuan Wang

doi:10.1038/srep19497

Tie-Jun Wang, Chuan Wang

Open Access

https://doi.org/10.1038/srep19497

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Abstract

Hyperentangled Bell-state analysis (HBSA) is an essential method in high-capacity quantum communication and quantum information processing. Here by replacing the two-qubit controlled-phase gate with the two-qubit SWAP gate, we propose a scheme to distinguish the 16 hyperentangled Bell states completely in both the polarization and the spatial-mode degrees of freedom (DOFs) of two-photon systems. The proposed scheme reduces the use of two-qubit interaction which is fragile and cumbersome, and only one auxiliary particle is required. Meanwhile, it reduces the requirement for initializing the auxiliary particle which works as a temporary quantum memory, and does not have to be actively controlled or measured. Moreover, the state of the auxiliary particle remains unchanged after the HBSA operation, and within the coherence time, the auxiliary particle can be repeatedly used in the next HBSA operation. Therefore, the engineering complexity of our HBSA operation is greatly simplified. Finally, we discuss the feasibility of our scheme with current technologies.

Highlights

H gh a phase shift θ is picked up on the coherent probe beam
In a one-sided cavity, due to the spin selection rule, the right circularly polarized light R and the left circularly polarized light L pick up two different phase shifts after being reflected from the QD-cavity system, and after two photons reflected by a cavity, the parity state of this photon pair in polarization degree of freedom (DOF) can be determined by measuring the state of the excess electron of the auxiliary QD without destroying the two-photon quantum system
We show that the complete differentiation of 16 hyperentangled Bell states in both polarization and spatial-mode DOFs for two-photon system can be efficiently achieved based on a two-qubit SWAP gate by using a three-level Λ -typle atom-cavity coupled unit interacting with single photons in reflection geometry

Summary

Introduction

H gh a phase shift θ is picked up on the coherent probe beam. With the action of the cross-Kerr nonlinearity, one can distinguish the even-parity states from the odd-parity states in spatial-mode DOF of a two-photon system without destroying the two-photon system in the other DOF. The description of the system using cavity quantum electrodynamics (QED) plays an important role for information exchange between static and flying qubits in quantum communication networks and it has been demonstrated that, even in the bad-cavity regime, a measurable nonlinear phase shift between single photons can be achieved in a cavity QED system[43] This nonlinearity can be realized by a variety of physical systems, such as a leaky resonator interacting with an atom or a quantum dot[44,45,46]. In 2015, Liu et al.[47] presented a scheme for the generation and analysis of hyperentanglement assisted by two nitrogen-vacancy (NV) centers in diamonds coupled with microtoroidal resonators In these schemes, the nonlinearity between the photons and the auxiliary particles is used to construct the two-qubit controlled-phase operations which plays a critical role in HBSA protocols.

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Conclusion