Wspólnotowy Serwis Informacyjny Badan i Rozwoju - CORDIS

Theoretical results on qubits and QIP

We have delivered theoretical results on various areas of quantum information processing (QIP)implementation. These results are published (or in the process) and have impact for future experiments on magnetic qubits, but also wider impact for solid state QIP devices, as described below:

i) Study of the continuous measurement of solid state qubits. This has yielded understanding of the fundamental decoherence effects induced by various measurement schemes into the qubits they are measuring has been reached. This is relevant for magnetic qubits probed by SQUIDs, but has rather wider impact in being applicable to other solid state qubit systems and devices.
ii) Understanding of the operation of a DC SQUID or large current-biased Josephson junction operating as a qubit measurement system, in particular the knock-on effects to the qubit of the intrinsic irreversibility of a current fed to the measurement apparatus. This has impact for the use of such SQUID systems in any quantum measurement scenario.
iii) Understanding of the behaviour of a microwave-driven solid state qubit subject to decoherence - the effect of the Rabi oscillation signal on the measurement apparatus. This has impact for any solid state system driven with an external classical oscillatory field. In particular, various useful parameters concerning the qubit and its environment can be extracted from this measurement scenario.
iv) Study of the readout process (continuous observation and single shot projection) for matter qubits. Conventional approaches to QIP assume the existence of single shot projective readout for qubits, so this is the ultimate aim for any qubit system.
v) Novel proposals for hybrid matter/optical QIP. In the short term it is important to simply get solid state qubits working. However, taking a longer term perspective and thinking about actual QIP devices and technology, it is likely that communication will come into play. Hybrid matter/optical QIP systems are likely to play a very important role here.
vi) Study of the probing of magnetic qubits using external thermal noise. This is a useful investigative technique for plotting out magnetic susceptibilities of qubits. The groundwork was done many years ago by one of the participants for SQUID systems - this work can be readily adapted for nanomagnets.
vii) New approaches to detection and quantum gates based on the interactions between magnetic qubits and a common microwave bus mode. This work can be applied to any solid state qubits that couple to microwaves. Further ideas continue to emerge in this area.

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