Abstract
Quantum coherence control is reinvestigated for a new physical insight in quantum nonlinear optics and applied for a wavelength-convertible quantum memory in a solid ensemble whose spin states are inhomogeneously broadened. Unlike typical atomic media whose spin decays are homogeneous, a spin inhomogeneously broadened solid ensemble requires a counter-intuitive quantum coherence control to avoid spontaneous emission-caused quantum noises. Such a quantum coherence control in a solid ensemble satisfying both near perfect retrieval efficiency and ultralong photon storage offers a solid framework to quantum repeaters, scalable qubit generations, quantum cryptography, and highly sensitive magnetometry. Here, the basic physics of the counter-intuitive quantum coherence control is presented not only for a fundamental understanding of collective ensemble phase control but also for a coherence conversion mechanism between optical and spin states involving Raman rephasing.
Highlights
Quantum coherence control in a lambda-type three-level optical ensemble has drawn much attention for various applications of quantum nonlinear optics over the last several decades, ranging from Kerr nonlinearity to quantum information, where a controlled coherence conversion (CCC) between optical and spin states plays a key role
Since the first modified photon echo protocol was proposed for quantum memories in a spin homogeneous Doppler medium[21], several methods have followed in the name of atomic frequency comb echoes[24,25], gradient echoes[26], and controlled double rephasing (CDR) echoes[22,23,29] mostly in solid media
Both near perfect retrieval efficiency and ultralong storage time are the most important properties to be satisfied for recursive operations such as in circuit-based quantum computing[38] and quantum repeaters for long-distance quantum communications[39]
Summary
Quantum coherence control in a lambda-type three-level optical ensemble has drawn much attention for various applications of quantum nonlinear optics over the last several decades, ranging from Kerr nonlinearity to quantum information, where a controlled coherence conversion (CCC) between optical and spin states plays a key role. In spin homogeneous media such as alkali atoms[4,7,8,10,11,15,16,17,18,19,20,21,32,40,42], the control pulse C must be the same as B, if they are collinear, for the transition 2 − 3 without R7,8,10,11,21, resulting in NDFWM signal e’ in the same frequency as A (see Fig. 1e).
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