Preservation of quantum correlations in a femtosecond light pulse train within an atomic ensemble

Abstract

In this paper, we examined a possibility of preservation of a substantially multimode radiation in a single cell of quantum memory. As a light source we considered a synchronously pumped optical parametric oscillator (SPOPO). As it was shown in [1][2][3][4], SPOPO radiation has a large number of the correlated modes making it attractive for the purposes of the quantum communication and computing. We showed that these correlations can be mapped on the longitudinal spin waves of the memory cell and be restored later in the readout light. The efficiencies of the writing and readout depend on the mode structure of the memory determined by a mechanism of the lightmatter interaction under consideration (the non-resonance Raman interaction) and by the profile of the driving light field. We showed that like the initial light pulse train, the restored one can be represented by a set of squeezed supermodes. The mapping of the quantum multimode correlations on the material medium offers opportunities to manipulate the quantum states within the memory cell followed by the reading of the transformed state.

Noiseless signal shaping and cluster-state generation with a quantum memory cell

“…In this section, a brief description of the quantum memory model based on the off-resonant Raman interaction of the quantum signal and classical driving fields with an ensemble of three-level atoms in the Λ-configuration is presented. Detailed construction of this model, developed by the same team of authors, can been found in [25].…”

“…It should be noted that the exact solutions (5)- (6) generate a phase rotation of the field oscillators. However, it can be quite easily compensated experimentally by adding phase-shift devices before and after the memory cell, as shown in [25]. Hence, Eqs.…”

“…Given that the form of the kernel G(t, t ′ ) depends on the shape of the driving F (t) and the field-medium interaction time T W , we can change the mode structure of the memory by varying these parameters. Usually, the memory settings are chosen to store as many modes of the signal as possible, that is, as many eigenvalues as possible in the expansion (16) should be close to (or better equal to) one and the rest differ little from zero [10,25]. Such a multimode operating regime helps to increase the information capacity of the cell.…”

“…In [25], the simplest case when the time profile of the driving had a form of a periodic sequence of N rectangular pulses with duration T 0 was analyzed. Here, we do not limit ourselves to a specific form of the driving while constructing equations and solutions to be able vary this parameter further.…”