Dynamics of a Raman coupled model: Entanglement and quantum computation

Abstract

The evolution of a Raman coupled three-level Λ atom with two quantized cavity modes is studied in the large detuning case; i.e. when the upper atomic level can be adiabatically eliminated. Particularly the situation when the two modes are prepared in initial coherent or squeezed states, with a large average number of photons, is investigated. It is found that the atom, after specific interaction times, disentangles from the two modes, leaving them, in certain cases, in entangled Schrödinger cat states. These disentanglement times can be controlled by adjusting the ratio between average numbers of photons in the two modes. It is also shown how this effective model may be used for implementing quantum information processing. Especially it is demonstrated how to generate various entangled states, such as EPR-and GHZ-states, and quantum logic operations, such as the control-not and the phase-gate.

Scheme for generating entangled states of two field modes in a cavity

“…(13) could be performed for δ = 1 and since |φ 1,2 span the whole atomic subspace, it holds for any initial state. By using squeezed states which may be more peaked around their meansN , the validity constrains are more easily fulfilled [25,37]. The similar splitting of the field state in phase space is present for a squeezed state.…”

“…However, there is a conflict; for larger amplitudes of the initial coherent states the approximations are better fulfilled, while the decoherence times are decreased. The validity of these approximations and decoherences have been studied in the literature [27,25,37]. The opposite limit of large detuning was already studied in [22] for generation of entangled coherent states.…”

“…Suggested preparation schemes of entangled coherent states have been covered in a large amount of articles [12]. The proposed methods can be divided into: free propagating waves and linear optical elements [19], Kerr non-linearities [20], trapped ions [21] and cavity QED [22,23,24,25,26].…”

Multiphoton resonances for all-optical quantum logic with multiple cavities

“…5), falling to ∼ 0.91 if no measurement is made. Some tuning of the energy levels may be achieved by Stark shifting the Rydberg states [48].…”

Cavity-state preparation using adiabatic transfer

“…In this section we will look at the "H" configuration, but other setups could also be considered. We will show how it is possible to create entangled Schrödinger cat states [23,24,25] by measuring the atomic state after the interaction. We introduce the atomic states…”