/How simple crystals can help pave the way for full-scale quantum computing (via Qpute.com)
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How simple crystals can help pave the way for full-scale quantum computing (via Qpute.com)

Vaccine and drug development, artificial intelligence, transportation and logistics, climate science—all of these are areas that could be transformed by the development of full-scale quantum computers. and, Explosive growth Quantum computing investment The last 10 years.

However, today’s quantum processors are relatively small, less than 100. Cubit — The basic components of a quantum computer. Bits are the smallest unit of information in computing, and the term qubit comes from the term “qubit.”

Early quantum processors were important to demonstrate the potential of quantum computing, but to enable globally important applications, Over 1 million qubits..

Our new research addresses the central issues at the heart of quantum computer scale-up. How do you move from controlling a few cubits to controlling millions?Under research Released today Science Advances introduces new technologies that may provide solutions.

What exactly is a quantum computer?

Quantum computers use qubits to hold and process quantum information. Unlike classical computer bits of information, qubits utilize natural quantum properties known as “superposition” and “entanglement” to perform calculations much faster than classical computers. increase.

Unlike the classic bits represented by 0 or 1, qubits can reside in the following locations: 2 State (that is, 0 and 1) at the same time. This is called the superposition state.

Demonstration by Google When others It shows that even today’s early-stage quantum computers can outperform the most powerful supercomputers on the planet in highly specialized (though not particularly useful) tasks.

Google’s quantum computer, built with superconducting air circuits, used only 53 qubits and was cooled in a high-tech refrigerator to temperatures close to -273 ° C. This extreme temperature is needed to remove heat that can cause errors in fragile cubits. Such demonstrations are important, but the current challenge is to build a quantum processor with more qubits.

At UNSW Sydney, a major effort is underway to create quantum computers from silicon, the same material used in everyday computer chips. Since traditional silicon chips are packed in billions of bits in thumbnail size, the possibility of building a quantum computer using this technology is very attractive.

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Building a quantum computer with traditional silicon technology could arrive sooner

Control problem

In a silicon quantum processor, information is stored in individual electrons and confined under a small electrode on the surface of the chip.Specifically, cubits are electronically coded spin.. It can be drawn as a small compass inside the electron. The compass needle can point north or south to represent the 0 and 1 states.

To set the qubits to overlap (both 0) When 1) For operations that occur in all quantum computations, the control signal must be directed to the desired qubit. For silicon qubits, this control signal is in the form of a microwave field, much like the one used to make a call over a 5G network. Microwaves interact with electrons and rotate their spins (compass needles).

Currently, each cubit requires its own microwave control field. It is sent to the quantum chip from room temperature to the bottom of the refrigerator with a cable near -273 ° C. Each cable carries heat, but it must be removed before it reaches the quantum processor.

With today’s state-of-the-art about 50 qubits, this is difficult but manageable. Current refrigerator technology can handle the heat load of cables. However, this is a major hurdle when using systems with more than 1 million qubits.

The solution is “global” control

An elegant solution to the challenge of delivering control signals to millions of spin qubits Proposed in the late 1990s.. The idea of ​​”global control” was simple. Broadcast a single microwave control field throughout the quantum processor.

A voltage pulse can be applied locally to the qubit electrode to allow individual qubits to interact with the global field (and create superpositions).

It is much easier to generate such voltage pulses on-chip than to generate multiple microwave fields. This solution requires only one control cable and eliminates the obstructive on-chip microwave control circuitry.

For over 20 years, global control of quantum computers has remained an idea. Researchers have been unable to devise the right technology to integrate with a quantum chip to generate a microwave field with the right low power.

Our research shows that a component known as a dielectric resonator may ultimately make this possible. A dielectric resonator is a small transparent crystal that traps microwaves for a short time.

Microwave trapping, a phenomenon known as resonance, allows microwaves to interact longer with spin qubits, significantly reducing the microwave power required to generate control fields. This was essential for operating the technology in the refrigerator.

In our experiments, we used a dielectric resonator to generate a control field in an area that could contain up to 4 million qubits. The quantum chip used in this demonstration was a 2-qubit device. We were able to show that the microwaves generated by the crystals can invert their respective spin states.

Diagram of a crystalline dielectric resonator generating a global control field in a spin quantum processor.
Tony Melov

The road to a full-fledged quantum computer

There is still work to be done before this technology reaches the task of controlling a million qubits. In our research, we were able to invert the state of the Cubit, but have not yet generated any superposition state.

Experiments are underway to demonstrate this important function. We also need to further investigate the effects of dielectric resonators on other aspects of the quantum processor.

However, we believe that these engineering challenges will eventually be overcome, clearing one of the biggest hurdles to achieving large-scale spin-based quantum computers.

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