Entanglement generation by interaction with semiclassical radiation

Abstract

We address a fundamental issue in quantum mechanics and quantum information theory, the generation of an entangled pair of qubits that interact solely through a third, semiclassical degree of freedom, in the framework of cavity quantum electrodynamics. We show that finite, though not maximal, entanglement is obtainable in the classical limit, at the price of a diverging effective interaction time. The optimal atomic entanglement derives from a trade-off between the atomic entanglement in a sub-wave packet and the purity of the atomic state. Decoherence by photon loss sets an upper limit on the degree of excitation of the cavity mode, beyond which the achievable entanglement decreases as the inverse mean photon number to the sixth power.Comment: 6 pages, 4 figure

Resonance phenomena in the interaction of a many-photon wave packet and a qubit

“…The asymptotic approximation (9) is not uniform in time. Nevertheless, the solution of equations (10)(11)(12) derived below is consistent with the approximation for all times ε −1 , and captures all the known phenomena of wave packet cavity QED in this time interval. We therefore proceed under the conjecture that the validity of the approximation can be extended to all orders for t ε −1 .…”

“…We therefore proceed under the conjecture that the validity of the approximation can be extended to all orders for t ε −1 . Note that unlike the semiclassical equations of motion generated by many-component Hamiltonians whose principal symbol is non-scalar [29,37], equation (10)(11)(12) are not flow equations of a classical Hamiltonian. In a companion work [36] we derive Hamiltonian equations of motion in an extended phase space that approximate the Heisenberg picture dynamics for times of o(ε −1/2 ).…”

“…The results of the previous subsection mean that CQED expectation values for highly excited initial states may be calculated using ( 6) by solving equations (10)(11)(12).…”

“…This is indeed the case for short times, where the field evolution is approximately classical and the qubit Rabi oscillates, but for longer times manifestly non-classical behavior takes place, including collapse-revival of the Rabi oscillations [6], and splitting of the electromagnetic field wave packet to create 'Schrödinger cat' states [7,8]. Nevertheless, these effects can be understood and described with high accuracy using semiclassical theories based on flow in generalized phase spaces [9,10].…”

Preparation and entanglement purification through two-step measurements

“…It is therefore desirable to prepare entangled states, such as, for instance, the Bell state from some mixed states. There are a lot of methods proposed theoretically and experimentally [3][4][5][6][7][8][9][10][11][12][13][14][15][16]. A very simple but robust method to produce an entangled resource was proposed in 2003 [17].…”