Simple Crystal Pave Full-Scale Quantum Computing
The development of a quantum computer on a large scale will transform many areas, including vaccine and drug development, artificial Intelligence, transport and logistics, and climate science. Over the past decade, quantum computing investments have seen an explosion. However, quantum processors of today are very small in scale. They have fewer than 100 qubits, which are the fundamental building blocks of quantum computers. Qubits is the smallest unit in computing. It comes from quantum bits.
Although early quantum processors were crucial in demonstrating quantum computing potential, it is likely that processors with more than a million qubits will be require to realize globally important applications. New research addresses a fundamental problem in scaling up quantum computers. How can we control millions of qubits instead of just a few? We present a new technology in Science Advances that could offer a solution.
What Is A Quantum Computer Exactly?
Qubits are use to store and process quantum information in quantum computers. Qubits are able to do some calculations faster than classical computers, unlike classical computers’ bits of information.
A qubit, unlike a classical bit which can be represent by either 1 or 0, can exist in both 0 and 1 simultaneously. This is call a superposition state.
Google and other companies have demonstrated that even early-stage quantum computers can surpass the most powerful supercomputers in the world for a highly specialized task. This is what we call quantum supremacy.
Google’s quantum computer built using superconducting electrical components. It had 53 qubits. The temperature was close to -273 in high-tech refrigeration. This extreme temperature is necessary to remove heat which could cause errors in the fragile qubits. These demonstrations are important but the challenge is to create quantum processors that have many more qubits.
UNSW Sydney is making major efforts to create quantum computers using the same material as computer chips every day: silicon. The prospect of using this technology for building a quantum computer is exciting because a conventional silicon chip is small and can hold several billion bits.
Control Quantum Problem
Information store in silicon quantum processors by individual electrons. These electrons are located beneath small electrodes on the chip’s surface. The qubit coded into the spin of the electron is a specific example. You can imagine it as a tiny compass within the electron. The needle can point either north or south, representing the 0 and 1 states.
A control signal must be direct at the qubit to set it in superposition (both 0 & 1), which is a common operation in quantum computations. This control signal for qubits in silicon is in the form a microwave field. It’s similar to the ones used to transport phone calls over 5G networks. The electron spins (compass needle), when the microwaves interact with it.
Each qubit currently requires its own microwave control area. The microwave control field is deliver to the processor via a cable that runs from room temperature to the bottom of a refrigerator at around -273. Each cable carries heat, which must be remove before the cable reaches the quantum processor.
This is difficult, but it is possible at 50 qubits. The current refrigerator technology is capable of handling the heat load from cable. It is a major problem if we want to use systems with more than a million qubits.
Global Control Is The Solution
In the late 1990s, a simple solution was found to the problem of controlling millions of spin qubits. Global control was a simple concept: Broadcast one microwave control field over the whole processor.
To make qubit electrodes interact with the global fields (and create superposition states), voltage pulses can be applied to them locally.
It is much simpler to generate these voltage pulses on-chip that it is to generate multiple microwave field. This solution is simple and requires only one control cable. It also removes the obtrusive microwave control circuitry.
Global control over quantum computers has been an idea for more than 20 years. Researchers couldn’t find a technology that would allow for the integration of a chip to generate microwave fields at low power.
Our work shows that a component called a dielectric resonance could allow us to do this. A dielectric resonator, a transparent small crystal that traps microwaves for a brief period of time, is what we are referring to.
Resonance is a phenomenon that traps microwaves. This allows them to interact longer with spin qubits and reduces the power required to create the control field. This was crucial for operating the refrigerator’s technology.
Our experiment used the dielectric resonance to create a control field that covered an area that could hold up to four million qubits. This demonstration used a quantum chip with two qubits. We were able show that the microwaves generated by the crystal could flip each spin state.
The Road To A Quantum Computer On A Large Scale
This technology will not be able to control a million qubits. There are still many things to do. Our study showed that we were able to change the qubit state, but could not produce superposition states.
This critical capability is being demonstrated by ongoing experiments. Further research is needed to determine the effect of the dielectric resonance on other aspects and functions of the processor.
We believe that these engineering challenges can be overcome and will eventually lead to a large-scale spin-based quantum computing system.