Research has Found a Missing Piece of the Optical Quantum Computing Puzzle

A study from the McKelvey School of Engineers at St. Louis University in Washington discovered a missing component in the optical quantum computing challenge. Associate Professor Jung-Tsung Shen of the Faculty of Electrical and Systems Engineering has created a high-fidelity, two-bit, deterministic quantum logic gate using a novel type of light. This innovative logic gate outperforms current technologies by orders of magnitude. The distinctive properties of a quantum system’s capacity to hold a variety of distinct attributes, or states, and entangle two particles working as non-classically connected although physically separated are tied to quantum’s potential.

“Ideally, the fidelity can be as high as 97%,” Shen said.

In May 2021, his findings were published in Physical Review A. Whereas in a traditional computer, the value of a bit (a 1 or a 0) is determined by the voltage, researchers frequently use individual electrons as “qubits,” the quantum equivalent. Electrons have a number of characteristics that make them ideal for this task: They can be easily manipulated and interacted with by an electric or magnetic field. When two bits must be entangled in order for quantum physics to reveal itself, interaction is advantageous.

On a traditional computer, scientists frequently use the quantum equivalent “qubits” of individual electrons for determining a little’s value. Electrons have a lot of good qualities: they can be easily controlled by an electrical or magnetic field, and they interact. When two bits are required to depict the quantum physics wilderness, interaction is advantageous. Their desire to interact, on the other hand, is a source of anxiety. Anything can affect electrons, from stray magnetic fields to electrical lines, making them tough to handle.

In the last two decades, however, numerous scientists have attempted to use photons instead of electrons as qubits. If computers are to make a genuine impact, we must aim to build a platform that is light. Electrons are influenced by everything from stray magnetic fields to electrical lines, making them difficult to completely regulate. However, some scientists have been attempting to employ photons instead of electrons as qubits over the past two decades. “If computers are going to have a true impact, we need to look into creating the platform using light,” Shen said.

Photons have no charge, which can cause problems on both sides: they don’t interact with the environment like electrons, but they also don’t interact with one another. Ad-hoc (effective) inter-photon connections were also difficult to build and create. Or so traditional thinking went. The unusual properties of measurement are another bizarre manifestation of quantum physics. Quantum engineering isn’t difficult, but it’s full of surprises.

In less than a decade, scientists working on this problem have been able to measure two photons as they exit a logic gate, rather than having to get entangled as they would if they were. It acted in a certain way for me. Another wild expression of quantum mechanics is a unique property of measurement. “Quantum mechanics isn’t difficult, but it’s full of surprises,” Shen said.

The measuring breakthrough was significant, but not game-changing. Because only one pair of photons became entangled for every 1,000,000 photons, this is the case. Researchers have since been more successful, but, Shen said, “It’s still not good enough for a computer,” which has to carry out millions to billions of operations per second. Because of the discovery of a new type of quantum photonic states called photonic dimers, which are photons entangled in both space and frequency, Shen was able to design a two-bit quantum logic gate with such efficiency.

Researchers have been more successful since then, but Shen said, “Computers aren’t enough,” and they have to perform millions to billions of operations per second. Nothing happens when a single photon enters or exits a logic gate; it just passes in and out. But when there are two photons, “That’s when we predicted the two can make a new state, photonic dimers. It turns out this new state is crucial.” A logic gate for two-bit operations can be designed in a variety of ways mathematically. These various designs are referred to as comparable. The controlled-phase gate (or controlled-Z gate) is the specific logic gate that Shen and his research group created.

The controlled-phase gate’s main function is that the two photons that exit are in the negative state of the two photons that entered. When two photons (representing two optical qubits) enter the logic gate, they form a pair, “the logic gate design is such that the two photons can form a photonic dimer,” Shen said. “The new quantum photonic state turns out to be critical since it gives the initial state the proper sign, which is required for optical logic operations.” When a single photon passes through a logic gate, nothing happens. If two photons exist, they can combine to form a new photonic dimer. This is when we expected it to happen. This new ailment turns out to be crucial.

Shen collaborated with the University of Michigan to evaluate his concept as a moderate-temperature solid-state logic gate. So far, he says, the results appear to be promising. According to Shen, the result is perplexing to most individuals but evident to those who are knowledgeable.

“It’s like a puzzle,” he said. “It can be complicated to do, but once it’s done, a glance at it will tell you it’s right.”

In traditional circuits, there is no negative sign. The minus sign, on the other hand, exists and is critical in quantum computing. When two independent photons enter, the Logical Gate is designed in such a way that they can generate a photonic dimer. Because it enables for the proper signals for optical logic operations in the output state, the new quantum photonic state becomes crucial. Michigan University is putting its idea to the test as a logical solid-state door that can work in mild conditions. They think the findings are good so far; it’s like a puzzle.