The new quantum computer puzzle

Research from the McKelvey School of Engineering at Washington University in St. Louis has found the missing piece in the puzzle of quantum computers.

Jung-Tsung Shen, Associate Professor in the Department of Electrical and Systems Engineering developed a high-precision, high-accuracy two-bit quantum logic gate. which takes advantage of a new light This new logic gate is an order of magnitude more efficient than current technology.

“In the ideal case The accuracy could be as high as 97%,” Son said.

His research was published in May 2021

The potential of quantum computers is tied to the unusual properties of superpositions. That is the ability of a quantum system to have many different properties or states at the same time and entangle two particles acting as if they were interrelated in non-classical particles. Even though the body is separated

When the set voltage of bit (1 or 0) in a classic computer Researchers often use individual electrons as “qubits,” which are quantum equivalents. Electrons have a number of characteristics that are suitable for the job: they are easily controlled by electric or magnetic fields and interact with each other. Interactions are helpful when you need two bits to get involved—let the wilderness of quantum mechanics unfold.

But the inclination to interact is also a problem. Everything from stray magnetic fields to wires can influence electrons. making it truly difficult to control.

However, over the past two decades Some scientists have tried to use photons as qubits instead of electrons, Shen said, “if computers would have a real impact. We have to consider building a platform using light.

Photons are uncharged, which can lead to the opposite problem: they don’t interact with the environment like electrons. But there is no interaction with each other. It’s also a challenge to design and build ad-hoc photon interactions. (Effective) or the same idea goes on.

less than a decade ago Scientists working on this problem have discovered that although they do not become entangled when entering a logic gate, they are not intertwined. Measuring the two photons as they exited the system made them behave as if they were. The peculiarity of measurement is another phenomenon of quantum mechanics.

“Quantum mechanics is not difficult. but full of surprises,” Shen said.

The discovery of the measurement was a novelty. But it didn’t change the game at all. That’s because for every 1,000,000 photons, only one pair gets entangled. Researchers have had more success since then, but Shen said “it’s still not good enough for computers”, which must perform millions and billions of operations per second.

Shen was able to efficiently create two-bit quantum logic gates due to the discovery of a new type of quantum photonic state. That’s a photonic dimer. Photons are entangled in both space and frequency. His prediction of existence was validated by an experiment in 2013, and since then he has discovered a new application of this light.

When a single photon enters a logic gate Nothing remarkable happened—photons entered and exited. But when there are two photons “That’s when we predicted that the two could form a new state, photonic dimers. It turned out that this new state was important.”

mathematical There are several ways to design a logic gate for two bit operations. These different designs are called equivalents. The only logic gate that Shen and his research group designed was the control phase gate. The main function of the control phase gate is that the two photons that come out are in the negative state of the two photons that enter.

“In classical circuits there is no minus sign,” Shen said, “but in quantum computing. It turns out that the minus exists and is important.”

When two free photons (representing two optical cubits) into the logic gate. “The logic gate design allows both photons to form photonic dimers,” Shen said. There is the correct signal required for optical logic operation.”

Shen worked with the University of Michigan to test his design. which is a solid state logic gate which can work under moderate conditions So far, he said, the results seem positive.

Shen said this result, while largely puzzling. It is clear that those who know

“It’s like a puzzle,” he said. “It can be complicated to do. But when it’s done just look You will know that it is right.”