Ashfaq H. Khosa

Scalable cavity-QED-based scheme of generating entanglement of atoms and of cavity fields

We propose a cavity-QED-based scheme of generating entanglement between atoms. The scheme is scalable to an arbitrary number of atoms, and can be used to generate a variety of multipartite entangled states such as the Greenberger-Horne-Zeilinger,

Generation of Bell, NOON and W states via atom interferometry

W

An engineering two-mode field NOON state in cavity QED

, and cluster states. Furthermore, with a role switching of atoms with photons, the scheme can be used to generate entanglement between cavity fields. We also introduce a scheme that can generate an arbitrary multipartite field graph state.

Generating entangled states of continuous variables via cross-Kerr nonlinearity

We propose atom interferometric techniques for the generation of Bell, NOON and W states of an electromagnetic field in high-Q cavities. The fundamental constituent of these techniques is off-resonant Bragg diffraction of atomic de Broglie waves. We show good success probabilities for these schemes under the currently available experimental environment of atom interferometry.

Atomic state teleportation: from internal to external degrees of freedom

We generate highly non-classical entangled two-mode field states of the type (|n x , O y ) ± |0 x , n y 〉)/√2 by utilizing an atomic analogue of the Mach-Zehnder interferometer, where quantized fields in the high-Q cavities act as beam splitters and mirrors. We discuss that the probability for the production of the desired states may approach a value close to unity under presently available experimental conditions.

Generation of atomic momentum cluster and graph states via cavity QED

We propose a scheme for generating entanglement of quantum states with continuous variables (coherent states and squeezed vacuum states) of electromagnetical fields. The scheme involves cross-Kerr nonlinearity. It was shown that the cross-Kerr nonlinearity required for generating the superposition and entanglement of squeezed vacuum states is smaller than that required for coherent states. It was also found that the fidelity monotonously decreases with both the increase of the amplitude of the input coherent field and the increase of the deviation of the nonlinear phase shift from π.

Remote preparation of atomic and field cluster states from a pair of tri-partite GHZ states

We suggest a simple method to teleport an unknown superposition of the atomic internal state of a two-level atom onto transverse atomic momenta of another atom during its flight. The scheme relies on the standard cavity QED techniques and is inherently deterministic with sufficiently high fidelity for the teleported state. It is further shown that the procedure can be straightforwardly extended to remotely tune in the probability amplitudes of any atomic momenta multipartite entangled state.

REMOTE FIELD AND ATOMIC STATE PREPARATION

We present an experimentally feasible method, based on currently available cavity QED technology, to generate n-partite linear cluster and graph states in external degree of freedom of atoms. The scheme is based on first tagging n two-level atoms with the respective cavity fields in momentum space. Later on an effective Ising interaction between such tagged atoms, realized through consecutive resonant and dispersive interactions of auxiliary atoms with the remanent cavity fields, can generate the desired atomic momenta states. The procedure is completed when the auxiliary atoms after passing through Ramsey zones are detected in either of their internal states. We also briefly explain the generation of weighted graph states in the atomic external degree of freedom.

Measurement of the Wigner function via atomic beam deflection in the Raman–Nath regime

We propose two simple and resource-economical schemes for remote preparation of four-partite atomic as well as cavity field cluster states. In the case of atomic state generation, we utilize simultaneous resonant and dispersive interactions of the two two-level atoms at the preparation station. Atoms involved in these interactions are individually pair-wise entangled into two different tri-partite GHZ states. After interaction, the passage of the atoms through a Ramsey zone and their subsequent detection completes the protocol. However, for field state generation we first copy the quantum information in the cavities to the atoms by resonant interactions and then adapt the same method as in the case of atomic state generation. The method can be generalised to remotely generate any arbitrary graph states in a straightforward manner.

Quantum state measurement of any arbitrary entangled field-state via Ramsey interferometry

A scheme for remote preparation of field (atomic) states is proposed. Protocol execution requires cavity QED based atom-field interactions successively supplemented with Ramsey interferometry. The state to be remotely prepared at the receivers end is acquired by deterministically manipulating the senders component of the pre-shared entangled state. In the case of field entanglement, it is carried out with the help of an atom that passes through the senders cavity and then traverses a classical external field for specified times prior to detection. However, for atomic entangled states, only interactions with the classical field suffice to complete the task. The scheme guarantees good success probability with high fidelity and requires one bit of classical communication.