Superconducting Qubits RIKEN | UBC | Sherbrooke – In arXiv 0805.0164, Zagoskin and Blais provide a broad and accessible introduction to quantum information processing with superconducting qubits. "From a physicist's standpoint, the most interesting part of quantum computing research may well be the possibility to probe the boundary between the quantum and the classical worlds. The more macroscopic are the structures involved, the better. So far, the most "macroscopic" qubit prototypes that have been studied in the laboratory are certain kinds of superconducting qubits. To get a feeling for how macroscopic these systems can be, the states of flux qubits which are brought in a quantum superposition corresponds to currents composed of as much as 10⁵ - 10⁶ electrons flowing in opposite directions in a superconducting loop."

Efficient pulsed gates for an oscillator stabilized Josephson qubit IBM Watson In arXiv 0709.1478 and New J. Phys. 10 033027 (2008), Koch, DiVincenzo, Brito and Steffen derive operational specifications for high-fidelity one and two-qubit pulsed gates for a superconducting flux qubit, calculating the Hamiltonian with tunable interaction from initialization to readout.

"The quantitative fact that the values of gate infidelity are at the 1% level – and below – is the major result of this paper."

So, can a "debugged" IBM qubit be used soon for universal quantum computation?

"The short answer is, in our opinion, ultimately yes."

"The answer would certainly be no if the noise threshold for fault-tolerant quantum computation were in the neighborhood of the oft-quoted value of 10⁻⁵. It is not inconceivable for the experiment to get to these values someday, since we find that the infidelities decrease much faster than linearly with the assumed noise levels."

"To get to 10⁻⁵, we would need to get to the very daunting levels of 100nΦ₀ at 1Hz for the 1/f noise amplitudes and 100 f s for timing accuracies; there is optimism that both of these numbers are ultimately attainable. Fortunately, while 10⁻⁵ was the threshold as it was understood ten years ago, much recent work shows that with good designs, much higher thresholds are possible. According to Terhal and Burkard – 1% is, in fact, on the high end of the noise levels for which fault tolerance may be possible."

Photon transmission through sub-wavelength diameter apertures Delft | Optica In Optics Express 16, 10 (abstract, full article) and concurrent TU Delft summary, Photonics review, Adam, Planken et al. report on high time-resolution terahertz mapping of photon transmission through sub-wavelength diameter apertures:

"According to the laws of physics, it is particularly difficult to pass light through a hole smaller than half the wavelength of the light used." The Delft group conducted experiments using extremely high time-resolution measurements in the terahertz (THz) frequency range. The group discovered that even if the hole is up to fifty times smaller than the wavelength used, sufficient light can pass through to allow measurements near the hole – an extremely difficult task using other methods. "Improving the sharpness of THz microscopes, coupled with more sensitive detectors, will improve the viability of creating images of biological cells using this type of measurement."

Prior experiments at Leiden University (Nature 418, 304-306) have also studied photon transmission through sub-wavelength metal films and shown entanglement conservation to be much more robust than expected – surviving the conversion process from surface-plasmon waves, which tunnel through the barrier, before reradiating as photons on the opposite side of the film. "It's a good omen, because it's saying quantum entanglement can survive when you might not expect it to," says Bill Barnes, a photonics expert at the University of Exeter. "If they can survive this, what else can they survive?"

Time Reversal in Bose-Einstein Condensates Toulouse | CNRS In arXiv 0804.3514, Martin, Georgeot, and Shepelyansky of Quantware MIPS Center investigate time reversibility in Bose-Einstein condensates (BEC). "We show that inside the regime of quantum chaos, time-reversal dynamics can be inverted from explosion to collapse. The accuracy of time reversal decreases with the increase of atom interactions inside BEC, until it is completely lost – though, surprisingly, quantum chaos helps to restore time reversibility. Existing experimental setups similar to Ryu, Behinaein, and Wayper can test the fundamental question of BEC time reversal discussed here."