Quantum breakthrough yields new material to make ‘qubits’

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For decades, the world has increasingly relied 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: mostly a pocket-sized piece aluminum, iron and lithium This is millionfold more powerful than the computers that controlled the Apollo 11 moon landing in 1969.

Advances in quantum technologies, harnessing the properties of quantum physics, promise to go a step further and revolutionize virtually all industry and daily life. The result could be more powerful and energy-efficient devices. But to do that, physicists have to get creative in how to exploit the strange way atoms interact with each other.

It turns out that atomic defects in certain solid crystals could be key to unlocking the potential of the quantum revolution, according to new discoveries by researchers from the Northeast. The defects are essentially irregularities in the way atoms are arranged to form crystalline structures. These irregularities could create the physical conditions to house something called a quantum bit, or qubit for short — a fundamental building block for quantum technologies, he says Arun BansilDistinguished University Professor in the Northeast Physics Department.

Qubits are fundamentally different from classic computer bits, which represent the most basic units of information in computing. But because both are made of impossibly small materials, they are subject to the forces at work in the mysterious and elusive world of nanoparticles.

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

Bansil and colleagues found that defects in a certain material class, particularly two-dimensional transition-metal dichalcogenides, contained the atomic properties conducive to the fabrication of qubits. Bansil says the results described in a published study naturerepresent a breakthrough of sorts, particularly in quantum sensing, and may 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,” says Bansil.

Transition-metal dichalcogenides have a variety of quantum properties that make them particularly attractive for scientific study, says Bansil. Researchers in this field have said that the unique materials “almost unlimited potential in various fields, including electronic, optoelectronic, sensor and energy storage applications.”

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

“When we looked at many of these materials, we ended up finding only a handful of viable defects — about a dozen or so,” says Bansil. “Here, both the material and the type of error are important, because in principle there are many types of error that can occur in any material.”

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

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To get a better understanding of 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. Classic computers use bits to perform calculations. When you do almost anything on a computer, you send it a series of instructions that activate a central processing unit, or CPU. The CPU consists of circuitry that uses electrical signals to instruct the entire computer to execute program instructions stored in the system’s memory.

These signals communicate using information that is encoded or packaged in bits. The information is represented numerically in one of two values: 0 or 1, which describe the states of various circuits as either on or off. All modern electronic devices work with circuit components that send and receive information by essentially manipulating those zeros and ones, says Bansil.

Qubits behave very differently than existing bits, thanks to not well understood quantum mechanical properties. What makes a qubit different is that its values ​​are floating, which means — and this is where it gets weird — they can be 0 and 1 at the same time. That’s because of something called overlaya core principle of quantum mechanics that states that a quantum system can exist in multiple states at a given point in time until it is measured.

Quantum information systems can use the instead probability that a qubit will be in one state or another when being measured or observed to make calculations.

“The unique thing about a quantum bit is that it can essentially encode two different states at the same time,” says Bansil. “You are able to store, in principle, a very large number of possibilities in very few qubits at the same time.”

The challenge for the researchers was to find qubits stable enough to be used, given the difficulties of finding the precise atomic conditions under which they can be materially realized.

The currently available qubits – especially those related to quantum computing – all operate at very low temperatures, which makes them incredibly fragile,” says Bansil. That’s why the discovery of defects in transition-metal dichalcogenides is so promising, he adds.

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