Construction of practical quantum computers radically simplified

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NQIT researchers at the University of Sussex have proposed an exciting new architecture for scalable ion trap quantum computing that could radically simplify the engineering challenge of building a large-scale quantum computer.

Quantum computers could solve certain problems - that would take the fastest supercomputer millions of years to calculate - in just a few milliseconds. They have the potential to create new materials and medicines, as well as solve long-standing scientific and financial problems. Universal quantum computers can be built in principle - but the technology challenges are tremendous, perhaps more difficult than manned space travel to Mars.

In a new paper published in Physical Review Letters, Dr Seb Weidt and Professor Winfried Hensinger and colleagues from the Ion Quantum Technology Group, present a fundamentally different approach for trapped-ion quantum computing that uses voltages and microwave fields to control the ions, rather than lasers. This new design is based on individually-controlled voltages applied to each logic gate location, analogous to a traditional transistor architecture within a classical computer processor. When implemented, it would allow a substantial reduction in the number of laser beams required and a simplification of the design of the “chip” used to hold the trapped-ion qubits.

As a first step towards this concept, they have demonstrated a versatile quantum gate based on a far-field microwave ion trap, with an impressively high fidelity of 98.5%. This is more than an order of magnitude improvement compared with the previous demonstration using this method and very close to the 99% required for fault-tolerant quantum computing.

This new proposed architecture, along with the far-field microwave ion trap result, puts the construction of large-scale quantum computers within reach of current technology.

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Professor Winfried Hensinger and Dr Seb Weidt
Professor Winfried Hensinger (left) and Dr Seb Weidt (right) working on the experiment that was used to validate their ground-breaking new approach by producing an ‘entangled’ quantum state of two ions with extremely low error rate.
diagram of a trapped-ion quantum computer
A trapped-ion quantum computer would consist of an array of X-junctions with quantum bits formed by individual ions that are trapped above the surface of the quantum chip (shown in grey). Individual quantum bits are manipulated simply by tuning voltages as easy as tuning a radio to different stations. Applying voltage V1 results in no quantum operation (blue zones), applying voltage V2 results in a quantum operation on a single quantum bit (green zones), applying voltage V3 results in a quantum operation ‘entangling’ two quantum bits (red zones). An arbitrary large quantum computer can be constructed based on this simple-to engineer approach.