Phys Rev A 86, 021801 (2012)

The transition between the quantum world of subatomic particles and atoms and the macroscopic world of everyday objects is a fascinating regime to consider, and can be investigated by transferring quantum states between ultracold atomic systems and mechanical oscillators. Swati Singh and colleagues from the University of Arizona in the United States have now found that under appropriate conditions, some hybrid optomechanical systems are described by an effective beam-splitter Hamiltonian. This is welcome news in the community because the beam-splitter Hamiltonian is a well-understood model for state transfer between systems. The researchers considered an atomic Bose–Einstein condensate trapped inside a Fabry–Pérot cavity with a suspended end mirror. By adiabatically eliminating the dynamics of the optical field within the cavity, they were able to describe the effective Hamiltonian for the coupling between the mirror and the condensate. The coupling arises because the condensate acts as a Bragg mirror as a result of density oscillations induced by the cavity field. Transfers of two different states were simulated under realistic experimental conditions. An exotic Schrödinger cat state was reported to achieve a lower fidelity of overlap than a standard coherent state. This is due to this state's higher susceptibility to the quantum noise of the optical field, which results in a faster decoherence. The authors suggest that by using squeezed quantum fluctuations, the fidelity of overlap could be improved.