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Entropy

Analysis of Controlled Rabi Flopping in a Double Rephasing Photon Echo Scheme for Quantum Memories

Rahmatullah Rahmatullah, Byoung Seung HAM

Published Sep 9, 2020• 0 citations
Publisher

Abstract

A double rephasing scheme of a photon echo is analyzed for inversion-free photon echo-based quantum memories using controlled Rabi flopping, where the Rabi flopping is used for phase control of collective atom coherence. Unlike the rephasing-caused π-phase shift in a single rephasing scheme, the control Rabi flopping between the excited state and an auxiliary third state induces coherence inversion. Thus, the absorptive photon echo in a double rephasing scheme can be manipulated to be emissive. Here, we present a quantum coherence control of atom phases in a double rephasing photon echo scheme for emissive photon echoes for quantum memory applications.

DOI
10.3390/e22091007

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•Jan 16, 2017•0 citations
A double rephasing scheme of a photon echo is analyzed for inversion-free photon echo-based quantum memories using controlled Rabi flopping, where the Rabi flopping is used for phase control of collective atom coherence. Unlike the rephasing-caused π-phase shift in a single rephasing scheme, the control Rabi flopping between the excited state and an auxiliary third state induces coherence inversion. Thus, the absorptive photon echo in a double rephasing scheme can be manipulated to be emissive. Here, we present a quantum coherence control of atom phases in a double rephasing photon echo scheme for emissive photon echoes for quantum memory applications.
A double rephasing photon echo is analyzed for inversion-free photon echo-based quantum memories using controlled Rabi flopping, where the Rabi flopping is used for phase control of atom coherence. Unlike the rephasing-caused pi-phase shift in a single rephasing scheme, the control Rabi flopping between the excited state and an auxiliary third state induces coherence inversion. Thus, the absorptive photon echo in a double rephasing scheme can be manipulated to be emissive via the controlled Rabi flopping. Here we present a quantum coherence control of atom phases in a double rephasing photon echo scheme for emissive photon echoes for quantum memory applications.
Photon echo-based quantum memory protocols presented over the last decade are primarily to solve the population inversion constraint in conventional photon echoes. In addition to population inversion, other major constraints limiting quantum memory applications are the low retrieval efficiency and short storage time, in which the importance of these factors has recently increased because of the challenges of the entangled qubit scalability and quantum repeaters. Here, I present, analyze and discuss the solution model for a Controlled Double Rephasing (CDR) echo protocol to satisfy non-inversion, near-perfect retrieval efficiency, and ultra-long storage time. In the CDR echo, a coherent Rabi pulse pair plays a key role for controlling both the ensemble phase and echo propagation direction, where the followings are the major results. Firstly, a counter propagating control Rabi pulse-pair-induced backward echo is free from echo reabsorption, resulting in a near perfect retrieval efficiency. Secondly, the control Rabi pulse pair induces an optical-spin coherence conversion like in the ultraslow light-based photon storage, resulting in a storage time extension up to spin decay time. Finally, the control Rabi flopping to a third state induces a π phase shift to the ensemble coherence, resulting in an emissive echo in the double rephasing scheme, where the π phase shift is due to optical-spin coherence conversion process. Conclusion: This study reveals that the control Rabi flopping in a three-level system applied to conventional photon echoes for storage time extension induces a π phase shift to the coher ent ensemble.
A controlled double rephasing (CDR) photon echo is analyzed for inversion-free photon echoes using controlled coherence conversion (CCC), where an optical Rabi flopping between an excited and an auxiliary ground states is used for atom phase control for emissive photon echoes. Unlike the rephasing mechanism in photon echoes, the CCC induces coherence inversion to the intrinsic absorptive echoes in a double rephasing scheme. Thus, the CDR echo protocol can be vastly applied for modified photon-echo quantum memories.
A near perfect, storage time-extended photon echo-based quantum memory protocol has been analyzed by solving the Maxwell-Bloch equations for a backward scheme in a three-level system. The backward photon echo scheme is combined with a controlled coherence conversion process via control Rabi flopping to a third state, where the control Rabi flopping collectively shifts the phase of the ensemble coherence. The propagation direction of photon echoes is coherently determined by the phase matching condition between the data (quantum) and the control (classical) pulses. Herein we discuss the classical controllability of a quantum state for both phase and propagation direction by manipulating the control pulses in both single and double rephasing photon echo schemes of a three-level system. Compared with their well-understood use for two-level photon echoes, the Maxwell-Bloch equations to a three-level system have a critical limitation regarding the phase change when interacted with an arbitrary control pulse area.
A near-perfect storage time-extended photon echo-based quantum memory protocol has been analyzed by solving the Maxwell-Bloch equations for a backward scheme in a three-level system. The backward photon echo scheme is combined with a controlled coherence conversion process via controlled Rabi flopping to a third state, where the control Rabi flopping collectively shifts the phase of the ensemble coherence. The propagation direction of photon echoes is coherently determined by the phase-matching condition between the data (quantum) and the control (classical) pulses. Herein, we discuss the classical controllability of a quantum state for both phase and propagation direction by manipulating the control pulses in both single and double rephasing photon echo schemes of a three-level system. Compared with the well-understood uses of two-level photon echoes, the Maxwell-Bloch equations for a three-level system have a critical limitation regarding the phase change when interacting with an arbitrary control pulse area.
A double rephasing photon echo scheme inherently satisfies no-population inversion condition for quantum memory applications, while the resultant absorptive coherence prohibits echo radiation out of the medium. To solve this absorptive echo problem, a controlled coherence conversion (CCC) has been proposed and demonstrated for the collective atom phase control converting an absorptive echo into an emissive one. The recent observations of absorptive photon echoes in double rephasing schemes, however, seemingly contradict the CCC theory. Here the rephasing process of individual ensemble atoms is investigated by using typical Gaussian light pulses to prove that the absorptive echo observations are due to imperfect rephasing-caused coherence leakage. Although the imperfect rephasing-cuased photon echoes has nothing to do with fidelity, the lower retrieval efficiency limits quantum memory applications due to potential eavesdropping caused by device-dependent loopholes or limited quantum error corrections in fault-tolerant quantum computing.