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UChicago scientists discover way to make quantum states last 10,000 times longer:
A team of scientists at the University of Chicago's Pritzker School of Molecular Engineering announced the discovery of a simple modification that allows quantum systems to stay operational—or "coherent"—10,000 times longer than before.
[...] Quantum states need an extremely quiet, stable space to operate, as they are easily disturbed by background noise coming from vibrations, temperature changes or stray electromagnetic fields.
Thus, scientists try to find ways to keep the system coherent as long as possible. One common approach is physically isolating the system from the noisy surroundings, but this can be unwieldy and complex. Another technique involves making all of the materials as pure as possible, which can be costly. The scientists at UChicago took a different tack.
[...] In tandem with the usual electromagnetic pulses used to control quantum systems, the team applied an additional continuous alternating magnetic field. By precisely tuning this field, the scientists could rapidly rotate the electron spins and allow the system to "tune out" the rest of the noise.
"To get a sense of the principle, it's like sitting on a merry-go-round with people yelling all around you," Miao explained. "When the ride is still, you can hear them perfectly, but if you're rapidly spinning, the noise blurs into a background."
This small change allowed the system to stay coherent up to 22 milliseconds, four orders of magnitude higher than without the modification—and far longer than any previously reported electron spin system. [...] The system is able to almost completely tune out some forms of temperature fluctuations, physical vibrations, and electromagnetic noise, all of which usually destroy quantum coherence.
Journal Reference:
Kevin C. Miao, Joseph P. Blanton, Christopher P. Anderson, et al. Universal coherence protection in a solid-state spin qubit [$], Science (DOI: 10.1126/science.abc5186)
(Score: 0) by Anonymous Coward on Saturday August 15 2020, @03:10PM (2 children)
uhm ... never heard of the term but it looks like the word resonance is a bit misleading here?
In reading the description it looks like the following is happening.
You have a sensor that detects noise. You have (target) noise that you would like to detect. The sensor can't detect the noise because it's too low to reach the threshold of the sensor.
You have some wide band white noise. The white noise is too low to be detected by the sensor as well. You introduce the white noise to the sensor.
There is constructive interference between the target noise and the white noise. Where this constructive interference occurs the intensity gets amplified enough to trigger the sensor and now you can get some information from sensor about the target noise. The rest of the white noise is below the threshold of the sensor so it doesn't get detected by the sensor.
You have to play with the white noise to get an optimal signal to noise ratio. Too much white noise and the sensor starts to pick up the noise and the noise may dominate resulting in a low signal to noise ratio. Too little and you won't get a strong enough signal.
Not sure how this is related to resonance as I have learned it ... looks more like constructive interference. Heck, one can argue that resonance results in constructive interference but when I think of resonance I think of an oscillating force or vibration where more vibrational force is added in a way that synchronizes with an existing periodic vibrational force resulting in the repeated amplification of the force magnitude during each period. Kinda like a positive feedback system? This doesn't look the same but I guess they use the term resonance here too.
(Score: 0) by Anonymous Coward on Saturday August 15 2020, @03:21PM
(this post was in response to the stochastic resonance reference)
(Score: 0) by Anonymous Coward on Saturday August 15 2020, @09:12PM
(same poster).
A good example of resonance that I think of would be like a swing. You thrust yourself forward on a swing and then you get swung back and then as you go forward you apply more force again. If you time your force properly the force you apply to the prior forward motion will compound efficiently. With each iteration the force compounds with the prior forward force resulting in larger and larger swings each time.
That's resonance. The compounding effect of a force being applied during each periodic iteration of an event.
In stochastic resonance there doesn't appear to be a compounding effect after each iteration of an event. It just looks like ... constructive interference occurs just once to boost the signal past a threshold while the noise stays below the threshold so that you can detect the signal. but, as I said, I guess they call that resonance as well.