Quantum computing with trapped ions, atoms and light
AIP CONF PROC 551 (2001) 158-172
Abstract:
We consider experimental issues relevant to quantum computing, and discuss the best way to achieve the essential requirements of reliable quantum memory and gate operations. Nuclear spins in trapped ions or atoms are a very promising candidate for the qubits. We estimate the parameters required to couple atoms using light via cavity QED in order to achieve quantum gates. We briefly comment on recent improvements to the Cirac-Zoller method for coupling trapped ions via their vibrational degree of freedom. Error processes result in a trade-off between quantum gate speed and failure probability. A useful quantum computer does appear to be feasible using a combination of ion trap and optical methods. The best understood method to stabilise a large computer relies on quantum error correction. The essential ideas of this are discussed, and recent estimates of the noise requirements in a quantum computing device are given.Realising quantum computing: Physical systems and robustness
(2001) 199-206
Abstract:
The physical realisation of a large quantum computer, i.e. one which could perform calculations beyond the capabilities of classical computers, is discussed, It is necessary to consider both the physical mechanisms of the hardware and the noise tolerance of quantum error correction (QEC) methods, Estimates for noise tolerance which involve fewer simplifying assumptions than were previously employed are given, and the scaling of logic gate rate with logic gate precision is discussed. It is found that QEC is fast compared to methods such as adiabatic passage.Measurement of the lifetime of the 3d 2D5/2 state in 40Ca+
Physical Review A - Atomic, Molecular, and Optical Physics 62:3 (2000) 1-10
Abstract:
We report a measurement of the lifetime of the 3d 2D5/2 metastable level in 40Ca+, using quantum jumps of a single cold calcium ion in a linear Paul trap. The 4s 2S1/2-3d 2D5/2 transition is significant for single-ion optical frequency standards, astrophysical references, and tests of atomic structure calculations. We obtain τ = 1.168±0.007 s from observation of nearly 64 000 quantum jumps during ∼32 h. Our result is more precise and significantly larger than previous measurements. Experiments carried out to quantify systematic effects included a study of a previously unremarked source of systematic error, namely, excitation by the broad background of radiation emitted by a semiconductor diode laser. Combining our result with atomic structure calculations yields 1.20±0.01 s for the lifetime of 3d 2D3/2. We also use quantum jump observations to demonstrate photon antibunching, and to estimate background pressure and heating rates in the ion trap. ©2000 The American Physical Society.Speed of ion-trap quantum-information processors
Physical Review A - Atomic, Molecular, and Optical Physics 62:4 (2000) 042305-042301
Abstract:
The speed limit at which general processing operations can be driven in the ion-trap system was theoretically and experimentally studied. Focus was on the intrinsic limitations imposed by the physics of the system, such as the tightness of the trap and the presence of a rich energy-level structura in the vibrational modes. The obtained data were analyzed in detail.Speed of ion-trap quantum-information processors
Physical Review A American Physical Society (APS) 62:4 (2000) 042305