coherence time


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coherence time

[kō′hir·əns ‚tīm]
(physics)
The average time required for the relative phase of two waves, or the phase of a single wave, to fluctuate appreciably.
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The channel is assumed to be an ideal block-fading channel, i.e., channel values are invariant for the channel coherence time [T.sub.C].
Project participants will not only be tackling coherence time and integration--two of the issues plaguing quantum annealing machines, which are expected to be a breakthrough in terms of providing fast solutions to combinatorial optimization problems, but also developing elemental technologies to succeed in the domestic production of a quantum annealing machine.
In a demonstration of a part of a quantum memory device, scientists at Tsinghua University in Beijing made a qubit consisting of a magnetically trapped, positively charged ytterbium-171 ion, which achieved a coherence time of more than 10 minutes.
Todd Holmdahl, who oversees the quantum project at Microsoft, said he envisioned a quantum computer as something that could instantly find its way through a maze."A typical computer will try one path and get blocked and then try another and another and another," he said."A quantum computer can try all paths at the same time." The trouble is that storing information in a quantum system for more than a short amount of time is very difficult, and this short"coherence time" leads to errors in calculations.
While the latest study does not detail a method to overcome this hurdle, it suggests that connecting individual qubits does not change coherence time.
The coherence time of his qubits, or the length of time they can maintain a superposition, is tens of microseconds--about 10,000 times the figure for those on D-Wave's chip.
where t is the coherence time and A is the Planck length.
Researchers estimated the lifetime and coherence time to be on the order of several microseconds, and found that sensitivity of the avian compass is enhanced by environmental noise, with long coherence times not required for navigation.
They were also able to achieve a fourfold prolonged coherence time of the light emission.
The intervals between transmissions of the same symbol should be at least the coherence time so that different copies of the same symbol undergo independent fading.
"Active optical clocks provide several new possibilities of applications: (i) more stable optical clock than any current atomic clocks; (ii) sub-natural linewidth laser spectroscopy; (iii) long coherence time laser with linewidth at mHz level; (iv) Ramsey laser combining stimulated emission process and Ramsey separated oscillatory fields method," commented Professor Yiqiu Wang.