Quantum communication and computing with atomic ensembles using a light-shift-imbalance-induced blockade

Recently, we have shown that for conditions under which the so-called light-shift imbalance induced blockade occurs, the collective excitation of an ensemble of a multilevel atom can be treated as a closed two-level system. In this paper, we describe how such a system can be used as a quantum bit (qubit) for quantum communication and quantum computing. Specifically, we show how to realize a controlled-NOT gate using the collective qubit and an easily accessible ring cavity, via an extension of the so-called Pellizzari scheme. We also describe how multiple, small-scale quantum computers realized using these qubits can be linked effectively for implementing a quantum internet. We describe the details of the energy levels and transitions in an ${}^{87}\mathrm{Rb}$ atom that could be used for implementing these schemes.

Figure 1

Schematic illustration of a three-level transition in each atom in an ensemble.

Figure 2

Schematic illustration of the relevant collective states and the corresponding transition rates. See text for details.

Figure 3

Summary of the LSIIB process in an ensemble. See text for details.

Figure 4

Illustration of the basic configuration for coupling two ensembles (top), and the requisite energy levels for each atom (bottom). See text for details.

Figure 5

(a) Schematic illustration of the single qubit state preparation in ensemble I. (b) Schematic illustration for the single qubit operation for ensemble II. See text for details.

Figure 6

(a) Illustration of the excitation step used to transfer the state of E-I to the cavity. (b) Schematic illustration of the pulses inside E-II to transform the cavity state to E-II. See text for details.

Figure 7

Schematic illustration of quantum communication between two quantum computer. See text for details.

Figure 8

(a) Schematic illustration of the Zeeman sublevels in the D1 manifold of ${}^{87}\mathrm{Rb}$ atoms that can be used to implement the proposed schemes. (b) Schematic illustration of the ${}^{87}\mathrm{Rb}$ transitions that can be used for demonstrating the LSIIB effect in a single cluster without a surrounding cavity. See text for details.

Figure 9

(a) Schematic illustration of the configuration that can be employed for testing the controlled-NOT operation using the ensemble LSIIB. (b) Illustration of the excitations that could be employed for confirming the controlled-NOT gate operation. See text for details.