Decoherence Effects on All-optical Quantum Information Processing

Harry J. Kimble

N. Lozano-Crisóstomo, M. A. González-Galicia, J. C. García-Melgarejo +1 more

In a recent study, N. Matsuda et al. [1] experimentally demonstrated the optical Kerr effect at the single photon level in optical fibers. This achievement strongly supports the feasibility of implementing optical quantum information processing (OQIP) based on the Kerr nonlinearity in optical fibers. Nevertheless, decoherence introduces significant techno logical limitations to the realization of OQIP in such systems. Consequently, a comprehensive understanding of decoherence is essential to develop practical mitigation strategies. In the present work, we examine the loss of phase coherence, called classical decoherence, through a two-step process applied within each segment of a concatenated birefringent nonlinear single-mode optical fibers (BNLOFs). This investigation serves as a preliminary step toward establishing the foundational knowledge required for addressing quantum decoherence in BNLOFs. An analytical model describing classical decoherence of mixed polarization states in BNLOFs is developed, providing a classical analogue to the quantum decoherence phenomenon.

J. I. Cirac, Thomas Pellizzari, J. F. Poyatos +1 more

Jino Heo, Seong Gon Choi

We propose a photonic procedure using cross-Kerr nonlinearities (XKNLs) to encode single logical qubit information onto four-photon decoherence-free states. In quantum information processing, a decoherence-free subspace can secure quantum information against collective decoherence. Therefore, we design a procedure employing nonlinear optical gates, which are composed of XKNLs, quantum bus beams, and photon-number-resolving measurements with linear optical devices, to conserve quantum information by encoding quantum information onto four-photon decoherence-free states (single logical qubit information). Based on our analysis in quantifying the affection (photon loss and dephasing) of the decoherence effect, we demonstrate the experimental condition to acquire the reliable procedure of single logical qubit information having the robustness against the decoherence effect.

Min-Sung Kang, Jino Heo, Seong Gon Choi +2 more

We present an optical scheme for a SWAP test (controlled swap operation) that can determine whether the difference between two unknown states (photons) using cross-Kerr nonlinearities (XKNLs). The SWAP test, based on quantum fingerprinting, has been widely applied to various quantum information processing (QIP) schemes. Thus, for a reliable QIP scheme, it is important to implement a scheme for a SWAP test that is experimentally feasible. Here, we utilize linearly and nonlinearly optical (XKNLs) gates to design a scheme for a SWAP test. We also analyze the efficiency and the performance of nonlinearly optical gates in our scheme under the decoherence effect and exhibit a technique employing quantum bus beams and photon-number-resolving measurements to reduce the effect of photon loss and dephasing caused by the decoherence effect. Consequently, our scheme, which is designed using linearly optical devices and XKNLs (nonlinear optics), can feasibly operate the nearly deterministic SWAP test with high efficiency, in practice.

Masahiro Takeoka, Masahide Sasaki