Scientists come closer to building quantum computer capable of solving virtually any equation

March 24, 2021

The field of quantum computing is poised to take a leap forward. (AP Photo/Seth Wenig)

Researchers at the National Institute of Standards and Technology used fiber-optic wires to monitor and measure a basic unit of quantum information, a step toward building a computer that could one day process complex codes and high-level mathematical formulas with the help of quantum mechanics.

The study, published in Nature on March 24, brought scientists from the quantum and optical physics fields together to perform tests on qubits, elementary particles that store information for quantum computing — the equivalent of the bits used in ordinary computers. Previously, it was only possible to store qubits in systems powered by metal-based coaxial cables, which are less efficient and prone to overheating.

The experiment required researchers to translate light particles into microwave pulses that could measure and interact with the qubit by matching its resonant frequency, the oscillation rate at which qubits can shift between excited and ground states.

"I hadn't really thought about using [optical technology] for qubits until the conversations at the coffee bar started. Can optics bring anything to bear on this problem?" Frank Quinlan, an NIST researcher who focuses on optical technology, recalled asking his colleagues. "Having folks nearby that you run into and just talk about things — experiments are born out of that."

Traditional computers operate using a binary system, in which each piece of data can be represented with a zero or one. But quantum computers incorporate unique properties, such as the theory of superposition, to occupy the zero and one positions simultaneously. 

And while standard computers solve problems by trying out all possible options before determining the correct path forward, quantum computers have the advantage of testing multiple paths at the same time. If more qubits are added to the system, a quantum computer's power increases exponentially, laying the groundwork for systems capable of interpreting algorithms that would otherwise take hundreds of years to solve.

Current quantum computers are helpful for answering theoretical questions, but they are not yet capable of performing practical organizational or mathematical tasks. 

The NIST study, for instance, was conducted in a highly controlled laboratory setting with one laser interacting with one qubit — more of a proof of concept than a feasible tool. Florent Lecocq, a research associate at NIST who helped author the paper, said that although scientists are moving at a steady clip, the practical application of quantum computers could still take a few decades. 

"The prediction, as of today with the current technology, is that to make a useful quantum computer, we're going to need about a million qubits," Lecocq told The Academic Times. "Once you have that, you get into the realm of being able to do simulations of chemical reactions that we cannot do with regular computers." 

These simulations could offer chemists new insight into how substances operate on a quantum level, a realm that is notoriously difficult to track and observe. Google, IBM and various government bodies hope to utilize quantum computers for cracking high-level cryptographic codes and solving complex mathematical equations.

Although there are different methods for placing particles in superposition, the scientists at NIST created their system using superconductor technology, which must take place at temperatures that approach absolute zero, the lowest possible temperature, at –273.15 degrees Celsius or –459.67 degrees Fahrenheit. But superconductors usually rely on energy-intensive refrigerators to maintain low temperatures. 

Since qubits lose their superposition when exposed to light, the use of fiber cables might at first appear counterintuitive. But the benefits of utilizing fiber technology like the kind used in high-speed internet networks are two-fold: Glass and plastic-based fibers are capable of carrying data at higher speeds than traditional coaxial cables, and they also are better equipped to handle the cryogenic temperatures needed to maintain most superconductive systems.

The team discovered that the system could accurately identify the qubit's state 98% of the time, which was an equivalent rate to ordinary coaxial technology. Next, they intend to scale up their operation to see how multiple qubits will react under the same conditions.

The researchers found success not by uncovering a new, hidden mechanism for transforming energy but by instead reevaluating technologies that are already widely available, according to NIST physicist John Teufel. The scientists' approach also allowed them to magnify the behavior of a single particle to more easily spot its quantum properties.

"It's amazing that you can take this everyday technology and make it behave quantum mechanically like an individual atom or an electron," Teufel said. "That's somehow the surprising part and a lot of what the frontier encompasses."

The study, "Control and readout of a superconducting qubit using a photonic link" published March 25 in Nature, was authored by John D. Teufel, Scott A. Diddams, Katarina Cicak, Florent Lecocq, Frank Quinlan, and Joe Aumentado, National Institute of Standards and Technology.

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