Microwave Qubit Creation Method Smooths the Way for Large-Scale Quantum Computers

February 02, 2017 by Robin Mitchell

Researchers from the University of Sussex have created a new method for producing and controlling qubits which may bring quantum computers closer to reality.

Researchers from the University of Sussex have created a new method for producing and controlling qubits—and it's led to the first truly accessible plan for a real-world quantum computer made from available tech.

Quantum computers will play a vital role in society as they will provide significantly reduced computational times, efficient algorithm solving, and improved security. But if quantum computers are so great and highly sought after, why are they not available?

The truth is that billions upon billions of dollars (as well as some of the greatest minds) have been thrown at the quantum world but the quantum computer is still confined to the laboratory setup. Unlike classical computers which rely on bits storing ‘1’ and ‘0’, qubits store quantum information. So far, qubits have generally been created in labs using various methods and various materials.

Qubit creation and the study of concepts like quantum entanglement have thus far only been possible in the controlled spaces of laboratories. But researchers at the University of Sussex are trying to take quantum computer technology out of the realm of academia and into the hands of researchers everywhere. 


Qubit Creation: Voltage Instead of Lasers

While there are multiple methods of creating qubits and performing quantum calculations, one method that shows significant promise is the use of trapped ions. Typically, two lasers are directed towards an individual ion which creates a trapped ion (i.e., a charged atom) which can be used as a qubit. However, two lasers are needed per qubit which means a quantum computer with any real power—billions of qubits—would need billions of lasers which is clearly not practical.

However, this is where the University of Sussex comes in as researchers there have found a new production method that could really be the spark to set off the quantum computer race.


Lasers are a commonly used for qubit creation. Image courtesy of astroshots24

Researchers at the University of Sussex have successfully created qubits without the need of laser pairs to focus on ions. Instead, the ions, which sit on top of the ‘quantum chip’, are exposed to both a magnetic field gradient as well as a microwave field. Then, individual ions can be moved towards and away from other ions on the chip using voltages. This movement of ions is crucial in the design as the movement of the ions allows qubits to interact with each other or to be separated.

This work has been led by Professor Winfried Hensinger and Dr. Sebastian Weidt at the Ion Quantum Technology research group at the Sussex Centre for Quantum Technologies.


Professor Hensinger and Dr. Weidt. Image courtesy of the University of Sussex


The voltage control has three main levels of voltage which can make the ions perform three different functions. The lowest voltage causes the ion to perform no logical function, the second voltage causes the ion to become a one-input quantum gate, and the third voltage causes the ion to interact with a neighbor ion and become a two-input quantum gate. According to the team, the quantum chip behaves more like an FPGA than a CPU in having programmable gates.

What makes this design very important is the fact that all the gates use the same magnetic and microwave fields in addition to being voltage-controlled. This makes the production of a quantum chip trivial in comparison to current methods of having to use highly precise lasers which need a target accuracy of 5um. The fact that the ions can be controlled by voltages means that interfacing a quantum chip with a classical electronic device could be as easy as connecting two standard devices (say, a microcontroller and serial memory device).


Proposed quantum chip utilizing multiple ions. Image courtesy of the University Of Sussex


Producing the needed magnetic field can be done using current carrying wires—but what about the microwave field? Does the field need to be perfect and precise? According to the team, neither phase uniformity or intensity need to be equal everywhere. The only major requirement of the field is that a reasonable amplitude is applied throughout the device. This further strengthens the argument that this quantum computer production technique could provide a foundation for all future quantum devices.


Blueprints for the Next Steps

This quantum chip creation method is already proving to be invaluable in the development of quantum computers. When it was announced, Professor Hensinger was quoted as saying "We will construct a large-scale quantum computer at Sussex making full use of this exciting new technology." Now, mere months later, it's obvious that he's been busy.

Yesterday, Hensinger and Weidt (working with an international team and the British government) published a paper in Science Advances detailing a plan to use quantum computer modules to network together into a scalable quantum computer. This "blueprint" is the first of its kind as a clear and feasible path towards a working quantum computer.

The paper emphasizes that the research into replacing lasers in quantum chip creation is vital. The simple application of voltage to create the chips, paired with the use of an architecture that utilizes modern silicon fabrication techniques, means that companies and governments around the world would likely be able to create such module-based quantum computers with relative ease. The result could be accessible—and possibly remarkably powerful—quantum computers.

Read the new paper in Science Advances here.


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