Quantum memory atomic

Photons in quantum optical cavities also constitute excellent qubit candidates [52]. Resonant coupling of atoms with a single mode of the radiation field was experimentally achieved 25 years ago [53], and eventually the coherent coupling of quantum optical cavities with atoms or (simple) molecules was suggested as a means to achieve stable quantum memories in a hybrid quantum processor [54]. There might be a role to play for molecular spin qubits in this kind of hybrid quantum devices that combine solid-state with flying qubits. 

The advantages of enhanced coupling between collective many-atom states and the radiation field have to be checked against the worry that these states are highly entangled if non-classical fight is stored. Entangled states are known to be very sensitive to decoherence and one could naively expect their lifetime to decrease with the number of atoms. It is therefore important to analyze the effect of unwanted environmental influences on the fidelity of the collective quantum memory. 

Thus the decoherence model of Fig. 8 exactly reproduces the anticipated behavior. All decoherence processes resulting from individual and uncorrelated reservoir interactions of the atoms are either exponentially suppressed by the energy gap (33) or are proportional to l/N. The latter is due to the large effective distance of the collective states in state space. In this way a quasi decoherence free subspace of dimension two is generated which allows to protect a stored photonic qubit from decoherence much more efficiendy than possible in quantum memories based on single particles. 

Phase-dependent coherence and interference can be induced in a multi-level atomic system coupled by multiple laser fields. Two simple examples are presented here, a three-level A-type system coupled by four laser fields and a four-level double A-type system coupled also by four laser fields. The four laser fields induce the coherent nonlinear optical processes and open multiple transitions channels. The quantum interference among the multiple channels depends on the relative phase difference of the laser fields. Simple experiments show that constructive or destructive interference associated with multiple two-photon Raman channels in the two coherently coupled systems can be controlled by the relative phase of the laser fields. Rich spectral features exhibiting multiple transparency windows and absorption peaks are observed. The multicolor EIT-type system may be useful for a variety of application in coherent nonlinear optics and quantum optics such as manipulation of group velocities of multicolor, multiple light pulses, for optical switching at ultra-low light intensities, for precision spectroscopic measurements, and for phase control of the quantum state manipulation and quantum memory. 

HyperChem can perform quantum mechanics MO calculations on molecules containing 100 or more atoms. There is no restriction on the number of atoms, but larger structures may require excessive computing times and computer main memory. 

TOWARDS QUANTUM CONTROL OF LIGHT SHAPING QUANTUM PULSES OF LIGHT VIA COHERENT ATOMIC MEMORY... 

Metcalf H 1997 "Laser cooling as a form of optical pumping in the quantum domain of atomic motion , in "George W. Series Memorial Essays , Phys. Scripta T70 Topical Issue (ed. A Comey, J N Dodd, L R Pendrill and D N Stacey) in press... 

Electrons residing in molecular clusters can be viewed as microscopic probes of both the local liquid structure and the molecular dynamics of liquids, and as such their transitory existence becomes a theoretical and experimental metaphor for one of the major fundamental and contemporary problems in chemical and molecular physics, that is, how to describe the transition between the microscopic and macroscopic realms of physical laws in the condensed phase. Since this chapter was completed in the Spring of 1979, several new and important observations have been made on the dynamics and structure of e, which, as a fundamental particle interacting with atoms and molecules in a fundamental way, serves to assist that transformation for electronic states in disordered systems. In a sense, disorder has become order on the subpicosecond time-scale, as we study events whose time duration is shorter than, or comparable to, the period during which the atoms or molecules retain some memory of the initial quantum state, or of the velocity or phase space correlations of the microscopic system. This approach anticipated the new wave of theoretical and experimental interest in developing microscopic theories of... 

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