Coherent quantum state storage and transfer between two phase qubits via a resonant cavity
Abstract
As with classical information processing, a quantum information processor requires bits (qubits) that can be independently addressed and read out, longterm memory elements to store arbitrary quantum states, and the ability to transfer quantum information through a coherent communication bus accessible to a large number of qubits. Superconducting qubits made with scalable microfabrication techniques are a promising candidate for the realization of a largescale quantum information processor. Although these systems have successfully passed tests of coherent coupling for up to four qubits, communication of individual quantum states between superconducting qubits via a quantum bus has not yet been realized. Here, we perform an experiment demonstrating the ability to coherently transfer quantum states between two superconducting Josephson phase qubits through a quantum bus. This quantum bus is a resonant cavity formed by an openended superconducting transmission line of length 7mm. After preparing an initial quantum state with the first qubit, this quantum information is transferred and stored as a nonclassical photon state of the resonant cavity, then retrieved later by the second qubit connected to the opposite end of the cavity. Beyond simple state transfer, these results suggest that a highqualityfactor superconducting cavity could also function as a useful shortterm memory element. The basic architecture presented here can be expanded, offering the possibility for the coherent interaction of a large number of superconducting qubits.
 Publication:

Nature
 Pub Date:
 September 2007
 DOI:
 10.1038/nature06124
 arXiv:
 arXiv:0709.2341
 Bibcode:
 2007Natur.449..438S
 Keywords:

 Condensed Matter  Mesoscale and Nanoscale Physics;
 Condensed Matter  Superconductivity
 EPrint:
 17 pages, 4 figures (to appear in Nature)