2021-04-20

Physicists have built a qubit that can be used to search for dark matter

By yqqlm yqqlm

It is reported that dark matter accounts for 85% of all matter in the universe.

Physicists have built a qubit that can be used to search for dark matter

“We know that there are A lot of substances, their composition is different from you and me,” said Fermilab scientist Aaron Chou, who is also the co-author of a paper on this new technology published in Physical Review Letters. “The nature of dark matter is a very compelling mystery, and many of us are trying to solve it.” In particular, scientists hypothesized that there are two kinds of subatomic particles-“axons” and “hidden photons” are the emergence of dark matter. Possible way.

It is understood that the technology demonstrated by the Fermi Lab team at the University of Chicago can make dark matter search 1000 times faster than previous methods.

Since the axon was proposed more than 30 years ago, physicists have made little progress in detecting axons.

Chou pointed out: “Experiments using traditional techniques are far from meeting the conditions we need to detect high-quality axon dark matter. The noise level is too high.”

But in the past In the past ten years, scientists have become more and more adept at using the properties of quantum mechanics to create new technologies. Quantum mechanics is the law that controls the strange behavior of particles at the smallest level in the universe. One of the achievements is the “qubit element”, that is, the quantum computing bit. They are extremely sensitive to even the smallest disturbances–and this is exactly what people want.

In the team’s new technology, qubits are designed to detect photons generated when dark matter particles interact with electromagnetic fields. A special device called a superconducting cavity provides a way to accumulate and store signal photons. The qubit is inserted into the cavity, and then the photon is measured.

This technology will help find any dark matter candidates, because invisible particles can be detected when they are converted into photons.

Physicists have built a qubit that can be used to search for dark matter(1)

Scientists say that this technology The key to sensitivity is its ability to eliminate false positive readings. Traditional technology destroys the photons they measure. But the new technology can detect photons without destroying it. Repeated measurement of the same photon within the life cycle of 500 microseconds can prevent false readings.

“Because it takes about 10 microseconds to measure a photon with a qubit, we can make about 50 repeated measurements of the same photon within the lifetime of the same photon.” Said Akash Dixit, the co-author of the research paper.

The technology of the Fermi Lab team at the University of Chicago also reduces the noise of the hidden signal.

Chou said: “This is a smarter and cheaper method that can also greatly increase sensitivity. Now that the level of static noise has been reduced a lot, you have the opportunity to see To very small fluctuations, this is due to very, very small signals.”

“Traditional methods will generate a noise photon for each measurement, and our detector will generate one for every thousand measurements. Noise photons,” Dixit pointed out.

Dixit and his colleagues borrowed from the technique of atomic physicist Serge Haroche (Serge Haroche), who won the 2012 Nobel Prize in Physics for this achievement .

The superconducting microwave cavity is the key to this new technology. The cavity used in the experiment is made of high-purity–99.9999%–aluminum. At extremely low temperatures, aluminum becomes superconducting, a feature that extends the lifespan of qubits, and the lifespan of qubits is essentially short-lived.

Dixit noted: “The benefit we get is that once you – or dark matter – put a photon into the cavity, it can hold the photon for a long time. The longer the cavity holds the photon. The longer it is, the longer it will take us to measure.”

The sensitivity of this technology to particles is 36 times the quantum limit of the traditional quantum measurement benchmark.

If axons exist, current experiments provide a one-tenth chance to detect photons produced by dark matter interactions.

“In order to further improve our ability to perceive such rare events, the temperature of photons needs to be lowered,” said David Schuster, associate professor of physics at the University of Chicago and co-author of the new paper. Lowering the photon temperature will further increase the sensitivity to all dark matter candidates, including hidden photons.

It is understood that the photons in the experiment were cooled to a temperature of about 40 milliliters (millikelvins), slightly above absolute zero. Researchers want to reduce the temperature to 8 milliliters. At this point, the environment for searching for dark matter will become spotless, and in fact there will be no background photons at this time.

“Although there is still a long way to go, we have reason to be optimistic,” Schuster said. “We are using quantum information science to help search for dark matter, but the same background photon is also a potential for quantum computing. Source of error. So the purpose of this research goes beyond basic science.”

Schuster pointed out that this project provides a good example of collaboration between university laboratories and national laboratories. “Our university’s laboratory has qubit technology, but in the long run, we cannot really conduct any type of dark matter search at the required level. This is where the national laboratory partnership plays an important role.”

The rewards of interdisciplinary effort can be huge. “Without the new technology we developed, there would be no way to do these experiments,” Chou said.