Quantum computing with trapped ions, atoms and light
Fortschritte der Physik 48:9-11 (2000) 839-858
Abstract:
We first consider the basic requirements for a quantum computer, arguing for the attractiveness of nuclear spins as information-bearing entities, and light for the coupling which allows quantum gates. We then survey the strengths of and immediate prospects for quantum information processing in ion traps. We discuss decoherence and gate rates in ion traps, comparing methods based on the vibrational motion with a method based on exchange of photons in cavity QED. We then sketch the main features of a quantum computer designed to allow an algorithm needing 106 Toffoli gates on 100 logical qubits. We find that around 200 ion traps linked by optical fibres and high-finesse cavities could perform such an algorithm in a week to a month, using components at or near current levels of technology.Measurement of the lifetime of the 3d 2D5/2 state in 40Ca+ -: art. no. 032503
PHYSICAL REVIEW A 62:3 (2000) ARTN 032503
Search for correlation effects in linear chains of trapped Ca+ ions
EUROPHYSICS LETTERS 51:4 (2000) 388-394
Efficient fault-tolerant quantum computing
Nature 399:6732 (1999) 124-126
Abstract:
Quantum computing - the processing of information according to the fundamental laws of physics - offers a means to solve efficiently a small but significant set of classically intractable problems. Quantum computers are based on the controlled manipulation of entangled quantum states, which are extremely sensitive to noise and imprecision; active correction of errors must therefore be implemented without causing loss of coherence. Quantum error-correction theory has made great progress in this regard, by predicting error-correcting 'codeword' quantum states. But the coding is inefficient and requires many quantum bits, which results in physically unwieldy fault- tolerant quantum circuits. Here I report a general technique for circumventing the trade-off between the achieved noise tolerance and the scale-up in computer size that is required to realize the error correction. I adapt the recovery operation (the process by which noise is suppressed through error detection and correction) to simultaneously correct errors and perform a useful measurement that drives the computation. The result is that a quantum computer need be only an order of magnitude larger than the logic device contained within it. For example, the physical scale-up factor required to factorize a thousand-digit number is reduced from 1,500 to 22, while preserving the original tolerated gate error rate (10-5) and memory noise per bit (10-7). The difficulty of realizing a useful quantum computer is therefore significantly reduced.Enlargement of calderbank-shor-steane quantum codes
IEEE Transactions on Information Theory 45:7 (1999) 2492-2495