Hidden symmetry can be key to ultra-powerful quantum computers

Researchers discover that hidden symmetry may be essential for more powerful quantum systems.

Researchers have found a way to protect very fragile quantum systems from noise, which can help design and develop new quantum devices, such as ultra-powerful quantum computers.

Researchers, from the University of Cambridge, have shown that microscopic particles can remain intrinsically bound, or entangled, over long distances even if there are random interruptions between them. Using the mathematics of quantum theory, they discovered a simple structure where entangled particles can be prepared and stabilized even in the presence of noise by taking advantage of a symmetry previously unknown in quantum systems.

Their results, reported in the journal Physical review letters, open a new window into the mysterious quantum world that could revolutionize future technology by preserving quantum effects in noisy environments, which is the single biggest obstacle to the development of such technology. Using this capability will be at the heart of fast quantum computers.

“Until we find a way to make quantum systems more powerful, their applications in the real world will be limited.” – Shovan Dutta

Quantum systems are built on the particular behavior of particles at the atomic level and can revolutionize the way complex calculations are performed. While a normal computer bit is an electrical circuit breaker that can be set to one or zero, a quantum or dome bit can be set to one, zero or both at the same time. Moreover, when two cubes are confused, an operation on one immediately affects the other, no matter how far apart they are. This dual state is what gives power to a quantum computer. A computer built with tangled cubes instead of normal bits can perform calculations beyond the capacity of even the most powerful supercomputers.

“However, qubits are incredibly small things, and the slightest noise in their environment can cause their clutter to break down,” said Dr Shovan Dutta of Cambridge Cavendish Laboratory, the paper’s first author. “Until we find a way to make quantum systems more powerful, their applications in the real world will be limited.”

Some companies – most importantly, IBM and Google – have developed working quantum computers, although so far these have been limited to less than 100 kbps. They require almost complete isolation from noise, and even then, have a very short lifespan of a few microseconds. Both companies plan to develop 1000 cubic quantum computers within the next few years, although if stability issues are not overcome, quantum computers will not achieve practical use.

Now, Dutta and his co-author Professor Nigel Cooper have discovered a powerful quantum system where multiple pairs of cubes remain entangled even with a lot of noise.

They modeled an atomic system in a lattice formation, where atoms interact strongly with each other, jumping from one lattice site to another. The authors found that if the noise increased in the middle of the lattice, it did not touch the tangled particles between the left and right sides. This surprising feature results from a special kind of symmetry that preserves the number of such tangled pairs.

“We did not expect this stabilized kind of mess at all,” Dutta said. “We encountered this hidden symmetry, which is very rare in these noisy systems.”

They showed that this hidden symmetry protects tangled pairs and allows their number to be controlled from zero to a large maximum value. Similar conclusions can be applied to a wide range of physical systems and can be realized with components already existing on experimental platforms, paving the way for controllable confusion in a noisy environment.

“Uncontrolled environmental concerns are bad for surviving quantum effects like clutter, but much can be learned by deliberately engineering specific types of concerns and seeing how particles react,” Dutta said. “We have shown that a simple form of anxiety can actually produce – and sustain – many confused couples, which is a great stimulus for experimental developments in the field.”

The researchers hope to confirm their theoretical findings with experiments within the next year.

Reference: “Long-range coherence and multiple stable states in a lost Qubit group” by Shovan Dutta and Nigel R. Cooper, December 9, 2020, Physical review letters.
DOI: 10.1103 / PhysRevLett.125.240404

The research was partially funded by the Engineering and Physical Sciences Research Council (EPSRC).

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