Quantum memory collective

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. 

Various schemes for hybrid quantum processors based on molecular ensembles as quantum memories and optical interfaces have been proposed. In Ref. [17], a hybrid quantum circuit using ensembles of cold polar molecules with solid-state quantum processors is discussed. As described above, the quantum memory is realized by collective spin states (ensemble qubit), which are coupled to a high-Q stripline cavity via microwave Raman processes. This proposal combines both molecular ensemble and stripline resonator ideas. A variant of this scheme using collective excitations of rotational and spin states of an ensemble of polar molecules prepared in a dipolar... 

My colleagues at the Quantum Chemistry Group and elsewhere, who organised and arranged a Banquet, with many surprise participants including students as well as old friends and family left an everlasting memory in me. The collected books, records and solvents add also to my spiritual education. 

This chapter covers message-passing, one of the primary software tools required to develop parallel quantum chemistry programs for distributed memory parallel computers. Point-to-point, collective, and one-sided varieties of message-passing are also discussed. 

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