A study at the McKelby Institute of Technology at Washington University in St. Louis found a missing part of the photon computing puzzle.
Jung-Tsung Shen, an associate professor in the Department of Electrical Systems Engineering, has developed a deterministic and fidelity 2-bit quantum. logic A gate that uses a new form of light. This new logic gate is orders of magnitude more efficient than current technology.
“In the ideal case, fidelity can be as high as 97%,” says Shen.
His study was published in the journal in May 2021 Physical Review A..
The potential of quantum computers is linked to the anomalous properties of superposition (the ability of a quantum system to contain many different properties or states at the same time) and the intertwining of two particles that function in a non-classical correlation. I will. Manners despite being physically separated from each other.
When a voltage determines the value of a bit (1 or 0) in a classical computer, researchers often use individual electrons as “qubits,” or quantum equivalents. Electrons have several properties that make them suitable for tasks. Electrons are easily manipulated and interact by electric or magnetic fields. Interactions are useful when you need to entangle two bits to reveal the wilderness of quantum mechanics.
But the tendency of their interaction is also a problem. Everything from stray magnetic fields to power lines affects electrons, which can make it difficult to truly control them.
However, for the past two decades, some scientists have tried to use photons as qubits instead of electrons. “If computers have a real impact, we need to consider using light to create a platform,” Shen said.
The opposite problem can occur because photons are uncharged. Photons do not interact with the environment like electrons, but they do not. It was also difficult to design and create ad hoc (effective) mutual designs.photon Interaction. Or so the traditional way of thinking went.
In less than a decade, scientists working on this issue have been able to measure two photons when they exit, without having to get entangled when entering a logic gate, as if they were. I found it to behave. A unique feature of measurement is another wild manifestation of quantum mechanics.
“Quantum mechanics isn’t difficult, but it’s full of surprises,” Shen said.
The discovery of the measurements was groundbreaking, but not at all. This is because for every 1,000,000 photons, only one pair was intertwined. 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.
With the discovery of a new class of quantum photonic states, photonic dimers intertwined in both space and frequency, Shen was able to construct a 2-bit quantum logic gate with such efficiency. His predictions of their existence were experimentally tested in 2013, and since then he has found this new form of use of light.
When a single photon enters the logic gate, nothing special happens. It goes in and out. But if you have two photons, “when you predicted that they could create a new state, the photonic dimer. This new state turned out to be important.”
Mathematically, there are many ways to design logic gates for 2-bit operations. These different designs are called equivalents. The specific logic gate designed by Shen and his research group is the control phase gate (or control Z gate). The main function of the control phase gate is to be in the negative state of two photons containing the two photons that come out.
“On a classic circuit, there is no minus sign,” Shen said. “However, Quantum computing, The minus sign is present and turns out to be important. ”
When two independent photons (representing two photon bits) enter the logic gate, “the logic gate design allows the two photons to form a photonic dimer,” Shen said. .. “The new quantum photonic state has proved to be very important because it allows the output state to have the correct sign, which is essential for optical logical operations.”
Shen has worked with the University of Michigan to test his design as a solid-state logic gate that can operate under moderate conditions. So far, he says, the results look positive.
Shen says the result is confusing to most people, but obvious to knowledgeable people.
“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.”
Zihao Chen et al, Two-photon control phase gate enabled by photonic dimer, Physical Review A (2021). DOI: 10.1103 / PhysRevA.103.052610
Washington University in St. Louis
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