explained | Are phonons, particles of sound, quantum too?

The movement of an insect on the surface of the water creates two sets of ripples that overlap each other, creating an interference pattern visible in the 11-12 o’clock area, New Mexico, May 29, 2019. | Image source: Mike Lewinsky/Unsplash

One of the hottest news in the world of computing these days is quantum computers (the other being artificial intelligence). Recently, IBM published paper which claimed to have proven that a quantum computer can solve a problem useful A problem that today’s traditional computers can’t, and it’s a consequence deserved by concerns that their computations can become too unreliable as they become too complex.

What are qubits?

Quantum computers use qubits as the basic units of information. A qubit can be a particle – like an electron; A collection of particles or a quantum system designed to behave like a particle. Particles can do funky things that large objects — like the semiconductors in classical computers — can’t because they are guided by the rules of quantum physics. These rules allow each qubit to have the values ​​”on” and “off” at the same time, eg.

The hypothesis of quantum computing is that information can be “encoded” into some property of a particle, such as the spin of an electron, and then processed using these strange capabilities. As a result, quantum computers are expected to perform complex computations beyond the reach of today’s best supercomputers.

Other forms of quantum computing use other units of information. For example, linear optical quantum computing (LOQC) uses photons and particles of light as qubits. Just like different pieces of information can be combined and manipulated by encoding them onto electrons and then making the electrons interact in different ways, LOQC demonstrates the use of optical equipment – such as mirrors, lenses, splitters, wave plates, etc. – with photons to process the information.

Indeed, any particle that can be controlled and manipulated using the phenomena of quantum mechanics must, on paper, be usable as a unit of information in a quantum computer.

What are phonons?

This is why physicists wonder if they can use phonons, too. Photons are packets of light energy. Similarly, phonons are packets of vibrating energy. So the question is: can we build a quantum computer whose unit of information is, colloquially, intact?

according to the paper Posted in Sciences This month, it should be possible.

The problem is that researchers can manipulate electrons with electric currents, magnetic fields, etc., and they can manipulate photons with mirrors, lenses, etc. – but what can they manipulate phonons with? To that end, in the new study, researchers from the University of Chicago report developing an acoustic beam splitter.

What is a beam splitter?

Beam splitters are widely used in optics research. Imagine a torch shining along a straight line. This is basically a stream of photons. When a beam splitter is placed in the path of light, it splits the beam in two: that is, it will reflect 50% of the photons to one side and allow the other 50% to pass straight through.

While it sounds simple, the working of a beam splitter is actually based on quantum physics. If you shine a million photons at it, it will produce two beams, 500,000 photons each. We can then reflect these two rays to intersect each other, creating an interference pattern (remember Young’s double-slit experiment). But the researchers found that the interference pattern appears even when they shine the photons in the beam splitter one by one. What photons are involved? The answer is themselves.

This is because a) particles can also behave like waves, and b) until an observation is made a quantum system exists in a superposition of all its possible states (such as a qubit being partly ‘on’ and partly ‘off’ at the same time) . So when a single wave interacts with a beam splitter, it goes into superposition of the two possible outcomes – reflected and transmitted. When these states combine, the Intervention style He appears.

What did the new study do?

In the new study, the researchers developed an acoustic beam splitter — a small comb-like device, with 16 metal rods protruding from it. It was placed in the middle of a 2 mm channel of lithium niobate. Each end of the channel had a superconducting qubit—a qubit whose circuit components were superconducting—that could simultaneously emit and detect individual phonons. The whole setup was kept at a very low temperature.

If these phonons were converted into sound, their frequency would be too high for humans to hear. Each phonon in the study, according to the paper, represents the “collective” vibration of about a quadrillion atoms.

The team found that these phonons interact with the comb just as photons interact with an optical beam splitter. When a phone emits from the left side of the channel, it is reflected half the time and transmitted to the right side the other half. When phonons were emitted simultaneously from the left and right sides, they ended up on one side (as expected).

Phone based computer…?

“The fundamental scientific question is whether phonons … actually behave the way quantum mechanics says they should,” said Andrew Cleland, a physicist at the Pritzker School of Molecular Engineering and a member of the study team. Physics magazine. His team’s tests prove that they do.

But it’s still a long way from here to a functional quantum computer that uses phonons as units of information. University of Nottingham physicist Andrew Armor put it more broadly Science newsWhat you’re doing is scaling [quantum] The Toolbox… people will build on it, it will last, and there’s no sign of it stopping anytime soon.”

• IBM has published a paper claiming to have proven that a quantum computer can solve a problem useful A problem that today’s traditional computers can’t, and it’s a consequence deserved by concerns that their computations can become too unreliable as they become too complex.

• The team found that these phonons interact with the comb just as photons interact with an optical beam splitter.

• Beam splitters are widely used in optics research. Imagine a torch shining along a straight line. This is basically a stream of photons. When a beam splitter is placed in the path of light, it splits the beam in two: that is, it will reflect 50% of the photons to one side and allow the other 50% to pass straight through.