Quantum breakthrough provides new material to make ‘qubits’

For decades, the world has become increasingly dependent on computers and sensors to do just about everything, and the technologies themselves are getting smaller, faster, and more efficient. Take your smartphone as an example: a pocket-sized piece of most aluminium, iron and lithium This is millions of times more powerful than the computers that guided the Apollo 11 moon landing in 1969.

Advances in quantum technologies, which deploy the properties of quantum physics, promise to go further and revolutionize almost all of industry and everyday life. The result could be more powerful and energy-efficient devices. But to do that, physicists have to get creative with how they exploit the strange ways atoms interact with each other.

It turns out that atomic defects in some solid crystals could be the key to unlocking the potential of the quantum revolution, according to new findings from Northeast researchers. Defects are essentially irregularities in the way atoms are arranged to form crystal structures. These irregularities could provide the physical conditions to house something called a quantum bit, or qubit for short, a fundamental building block of quantum technologies, according to Arun BansilUniversity Professor Emeritus in the Department of Physics at Northeastern.

Qubits are fundamentally different from classical computer bits, which are the most basic units of information in computing. But because both are made from incredibly small materials, they are subject to the forces operating in the enigmatic and elusive world of nanoparticles.

Arun Bansil, University Professor Emeritus in the Department of Physics at Northeastern Photo by Matthew Modoono/Northeastern University

Bansil and his colleagues found that the defects of a certain class of materials, in particular the two-dimensional transition metal dichalcogenides, contained the atomic properties conducive to making qubits. Bansil says the results, which are described in a study published in Naturerepresent a kind of breakthrough, especially in the field of quantum sensing, and can help accelerate the pace of technological change.

“If we can learn how to create qubits in this two-dimensional matrix, that’s a big, big deal,” Bansil says.

Transition metal dichalcogenides have a diverse range of quantum properties, which makes them particularly attractive for scientific research, says Bansil. Researchers in the field have said that the unique materials have “virtually unlimited potential in various fields, including electronic, optoelectronic, sensing and energy storage applications.

Using advanced calculations, Bansil and his colleagues sifted through hundreds of different material combinations to find those capable of hosting a qubit.

“When we looked at a lot of these materials, we ended up only finding a handful of viable defects, about a dozen or so,” says Bansil. “The material and the type of defect are important here, because in principle there are many types of defects that can be created in any material.”

The main conclusion of the study is that the so-called “antisite” defect in two-dimensional transition metal dichalcogenide films carries with it something called “spin”. Spin, also called angular momentum, describes a fundamental property of electrons defined in one of two potential states: up or down, says Bansil.

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To better understand what a qubit is and how it can be applied to future computers and sensors, it is important to understand how data is processed in existing “classic” computers. Conventional computers use bits to perform calculations. When you do almost anything on a computer, you send it a set of instructions that engages a central processing unit, or CPU. The processor is made up of circuitry that uses electrical signals to direct the entire computer to execute program instructions that are stored in system memory.

These signals communicate using encoded or bit-packed information. Information is represented numerically in one of two values: 0 or 1, which describe the states of various circuits as being on or off. All modern electronic devices work through circuit components that send and receive information by essentially manipulating these 0s and 1s, Bansil explains.

Qubits behave quite differently from existing bits, thanks to poorly understood quantum mechanical properties. What makes a qubit different is that its values ​​are fluid, which means – and this is where things get weird – they can be both 0 and 1 at the same time. It’s because of something called overlaya fundamental principle of quantum mechanics which states that a quantum system can exist in multiple states at any given time until it is measured.

Quantum information systems can instead use the probability that a qubit will be in either state when measured or observed to perform calculations.

“What’s unique about a quantum bit is that it can essentially encode two different states at the same time,” says Bansil. “You are able to basically store a very large number of possibilities in a very small number of qubits simultaneously.”

The challenge for researchers has been to find qubits that are stable enough to use, given the difficulties in finding the precise atomic conditions under which they can be materialized.

Currently available qubits, especially those involved in quantum computing, all operate at very low temperatures, which makes them incredibly fragile,” says Bansil. This is why the discovery of defects in transition metal dichalcogenides is so promising, he adds.

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Sherry J. Basler