Extending coherence times in superconducting qubits Schoelkopf Lab | via Leo DiCarlo — In arXiv 1105.4652, Schoelkopf et al  report novel implementation of a superconducting transmon qubit strongly coupled to a 5-cm, three-dimensional superconducting cavity, attaining reproducible extension in coherence times of both qubit (T₁ and T₂ > 10 μs) and cavity (T_cav ∼ 50 μs) by more than an order of magnitude compared to the current state-of-the-art superconducting qubits. "This enables the study of the stability and quality of Josephson junctions at precisions exceeding one part per million. Surprisingly, we see no evidence for 1/ f critical current noise. At elevated temperatures, we observe dissipation due to a small density (< 1 − 10 ppm) of thermally excited quasiparticles. These results suggest that the overall quality of Josephson junctions will allow for error rates of 10⁻⁴, approaching the error correction threshold to meet the DiVincenzo criteria for universal quantum computation. 





Time domain measurement of qubit coherence (a) Relaxation from |1⟩ of qubit J1. T1 is 60 μs for this measurement. (b) Ramsey fringes measured on resonance with (blue squares) and without (red squares) echo sequence. The pulse width for the π and π/2 pulses used in the experiments is 20 ns. An additional phase is added to the rotation axis of the second π/2 pulse for each delay to give the oscillatory feature to the Ramsey fringes.

The Quantum Computer is Growing Up: Robust error correction in a quantum processor Rainer Blatt | Innsbruck | Science | KurzweilAI 

A more efficient algorithm for error correction in quantum computers has been demonstrated experimentally by physicists at the Institute for Experimental Physics of the University of Innsbruck and the Institute for Quantum Optics and Quantum Information of the Austrian Academy of Sciences (IQOQI).

The physicists demonstrated the mechanism by storing three calcium ions in an ion trap. All three particles were used as qubits: one ion represented the system qubit while the other two ions represented auxiliary qubits. The system qubit was then entangled with the auxiliary qubits to transfer the quantum information to all three particles.

The physicists applied a quantum algorithm to determine whether an error occurred and, if there was an error, correct it. After making the correction, the auxiliary qubits were reset using a laser beam to enable repetitive error correction.

“For a quantum computer to become reality, we need a quantum processor with many quantum bits. Moreover, we need quantum operations that work nearly error-free; the third crucial element is an efficient error correction.”- Philipp Schindler

A team of physicists at the University of Innsbruck, led by Philipp Schindler and Rainer Blatt, has demonstrated a crucial element for quantum computers: repetitive error correction. This allows scientists to correct errors occurring in a quantum computer efficiently. The researchers recently published these findings in Science.