Scalable quantum computing with atomic ensembles

Sean D Barrett,Thomas M Stace,Peter P Rohde

doi:10.1088/1367-2630/12/9/093032

Sean D Barrett, Thomas M Stace + Show 1 more

Open Access

https://doi.org/10.1088/1367-2630/12/9/093032

Copy DOI

Abstract

Atomic ensembles, comprising clouds of atoms addressed by laser fields, provide an attractive system for both the storage of quantum information and the coherent conversion of quantum information between atomic and optical degrees of freedom. We describe a scheme for full-scale quantum computing with atomic ensembles, in which qubits are encoded in symmetric collective excitations of many atoms. We consider the most important sources of error—imperfect exciton–photon coupling and photon losses—and demonstrate that the scheme is extremely robust against these processes: the required photon emission and collection efficiency threshold is ≳86%. Our scheme uses similar methods to those already demonstrated experimentally in the context of quantum repeater schemes and yet has information processing capabilities far beyond those proposals.

Highlights

Atomic ensembles, comprising clouds of atoms addressed by laser fields, provide an attractive system for both the storage of quantum information, and the coherent conversion of quantum information between atomic and optical degrees of freedom
Duan et al (DLCZ) [1] showed that atomic ensembles could be used as nodes of a quantum repeater network capable of sharing pairwise quantum entanglement between systems separated by arbitrarily large distances
Amongst the more promising schemes for the implementation of scalable quantum computing are those in which qubits are stored in individual trapped atoms and entangled via single photon interference of photons emitted by the atoms [8, 9]

Summary

Effect of losses in EME state preparation

We consider the effect of loss at the lowest level of the protocol, i.e. when we try and make EME states of two ensemble qubits. In the final post selected state, we expect to see additional terms which correspond to excess excitations in the two ensembles This can be shown explicitly by considering the full network for the EME preparation protocol, together with the η-beamsplitters, tracing out the lost modes (i.e. those reflected from the η-beamsplitters) and projecting onto the case where only two detector clicks are observed.

Effect of loss in GHZ state preparation

Effect of loss in cluster state preparation and measurement based computation