Microsoft announces theoretical breakthough in pursuit of scalable quantum computers

Underlying physics of topological qubits has been proven, researchers say

Researchers at Microsoft have announced a scientific breakthrough in their pursuit of scalable quantum computers.

Unlike some of its competitors such as IBM, Honeywell and Google, which have built working quantum computers that use a small - albeit rapidly increasing - number of qubits (currently the record is somewhere over 200), Microsoft has instead focused its quantum computing efforts on an area known as topological qubits, in the hope that this approach will prove to be more scalable.

Qubits are extremely sensitive to their surroundings and any faults in the supporting hardware can cause decoherence of quantum entanglement. The larger the number of entangled qubits the harder it is to obtain long-term stability. It is thought that for a general purpose quantum computer, a few thousand qubits will be required.

Theoretically, topological qubits are more stable than those produced by traditional means, such as trapped ion technologies, as a result of using symmetries in the supporting material. Devices using these qubits should be more fault-tolerant and also more compact, with no loss of performance. Experiments using superconducting wires created from a variety of materials are being tested at Microsoft and elsewhere. However, until now, no-one had worked through the underlying physics to show that producing such qubits is feasible in the real world.

In a blog post, a team led by Dr Chetan Nayak at Microsoft says this hurdle has now been overcome. The researchers have been able to demonstrate that the underlying physics behind topological qubits are sound, and that they have observed a "topological gap" large enough to prove their point.

The topological gap is a measure of the stability of the qubit when it's in its topological state and capable of being used for computation. Identifying qubits that are in the topological state is very difficult using standard probes, but the Microsoft researchers have now achieved this by testing superconducting wires, and applying models that simulate the sorts of imperfections found in the superconducting materials used to create the qubits.

"Our team has measured topological gaps exceeding 30 μeV," they say in their blog.

"This is more than triple the noise level in the experiment and larger than the temperature by a similar factor. This shows that it is a robust feature. This is both a landmark scientific advance and a crucial step on the journey to topological quantum computation."

While this is a simulated result - no actual topological qubit has been produced - they insist that their results have been rigorously validated and checked by independent consultants.

With the theoretical underpinnings of topological qubits demonstrated, the next stage will be to create them in the lab and to test that they do indeed have the stability and speed advantages that the maths predict.

"We believe ultimately it will power a fully scalable quantum machine in the future, which will in turn enable us to realise the full promise of quantum to solve the most complex and pressing challenges our society faces," the post concludes.