# Hidden symmetry could be key to more robust quantum systems, researchers find

December 09, 2020Researchers have found a way to protect highly fragile quantum systems from noise, which could aid in the design and development of new quantum devices, such as ultra-powerful quantum computers.

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

Their results, reported in the journal

*Physical Review Letters*, open a new window into the mysterious quantum world that could revolutionise future technology by preserving quantum effects in noisy environments, which is the single biggest hurdle for developing such technology. Harnessing this capability will be at the heart of ultrafast quantum computers.

Quantum systems are built on the peculiar behaviour of particles at the atomic level and could revolutionise the way that complex calculations are performed. While a normal computer bit is an electrical switch that can be set to either one or zero, a quantum bit, or qubit, can be set to one, zero, or both at the same time. Furthermore, when two qubits are entangled, an operation on one immediately affects the other, no matter how far apart they are. This dual state is what gives a quantum computer its power. A computer built with entangled qubits instead of normal bits could perform calculations well beyond the capacities of even the most powerful supercomputers.

"However, qubits are extremely finicky things, and the tiniest bit of noise in their environment can cause their entanglement to break," said Dr Shovan Dutta from Cambridge's Cavendish Laboratory, the paper's first author. "Until we can find a way to make quantum systems more robust, their real-world applications will be limited."

Several companies - most notably, IBM and Google - have developed working quantum computers, although so far these have been limited to less than 100 qubits. They require near-total isolation from noise, and even then, have very short lifetimes of a few microseconds. Both companies have plans to develop 1000 qubit quantum computers within the next few years, although unless the stability issues are overcome, quantum computers will not reach practical use.

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

They modelled an atomic system in a lattice formation, where atoms strongly interact with each other, hopping from one site of the lattice to another. The authors found if noise were added in the middle of the lattice, it didn't affect entangled particles between left and right sides. This surprising feature results from a special type of symmetry that conserves the number of such entangled pairs.

"We weren't expecting this stabilised type of entanglement at all," said Dutta. "We stumbled upon this hidden symmetry, which is very rare in these noisy systems."

They showed this hidden symmetry protects the entangled pairs and allows their number to be controlled from zero to a large maximum value. Similar conclusions can be applied to a broad class of physical systems and can be realised with already existing ingredients in experimental platforms, paving the way to controllable entanglement in a noisy environment.

"Uncontrolled environmental disturbances are bad for survival of quantum effects like entanglement, but one can learn a lot by deliberately engineering specific types of disturbances and seeing how the particles respond," said Dutta. "We've shown that a simple form of disturbance can actually produce - and preserve - many entangled pairs, which is a great incentive for experimental developments in this field."

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

-end-

University of Cambridge

## Related Quantum Computers Articles from Brightsurf:

Optical wiring for large quantum computers

Researchers at ETH have demonstrated a new technique for carrying out sensitive quantum operations on atoms.

New algorithm could unleash the power of quantum computers

A new algorithm that fast forwards simulations could bring greater use ability to current and near-term quantum computers, opening the way for applications to run past strict time limits that hamper many quantum calculations.

A new technique prevents errors in quantum computers

A paper recently published in Nature presents a protocol allowing for the error detection and the protection of quantum processors in case of qubit loss.

New method prevents quantum computers from crashing

Quantum information is fragile, which is why quantum computers must be able to correct errors.

Natural radiation can interfere with quantum computers

Radiation from natural sources in the environment can limit the performance of superconducting quantum bits, known as qubits.

New model helps to describe defects and errors in quantum computers

A summer internship in Bilbao, Spain, has led to a paper in the journal Physical Review Letters for Jack Mayo, a Master's student at the University of Groningen, the Netherlands.

The first intuitive programming language for quantum computers

Several technical advances have been achieved recently in the pursuit of powerful quantum computers.

Hot qubits break one of the biggest constraints to practical quantum computers

A proof-of-concept published today in Nature promises warmer, cheaper and more robust quantum computing.

Future quantum computers may pose threat to today's most-secure communications

Quantum computers that are exponentially faster than any of our current classical computers and are capable of code-breaking applications could be available in 12 to 15 years, posing major risks to the security of current communications systems, according to a new RAND Corporation report.

Novel error-correction scheme developed for quantum computers

Experimental quantum computers are plagued with errors. Here Dr Arne Grimsmo from the University of Sydney and colleagues from RMIT and the University of Queensland offer a novel method to reduce errors in a scheme applicable across different types of quantum hardware.

Read More: Quantum Computers News and Quantum Computers Current Events

Researchers at ETH have demonstrated a new technique for carrying out sensitive quantum operations on atoms.

New algorithm could unleash the power of quantum computers

A new algorithm that fast forwards simulations could bring greater use ability to current and near-term quantum computers, opening the way for applications to run past strict time limits that hamper many quantum calculations.

A new technique prevents errors in quantum computers

A paper recently published in Nature presents a protocol allowing for the error detection and the protection of quantum processors in case of qubit loss.

New method prevents quantum computers from crashing

Quantum information is fragile, which is why quantum computers must be able to correct errors.

Natural radiation can interfere with quantum computers

Radiation from natural sources in the environment can limit the performance of superconducting quantum bits, known as qubits.

New model helps to describe defects and errors in quantum computers

A summer internship in Bilbao, Spain, has led to a paper in the journal Physical Review Letters for Jack Mayo, a Master's student at the University of Groningen, the Netherlands.

The first intuitive programming language for quantum computers

Several technical advances have been achieved recently in the pursuit of powerful quantum computers.

Hot qubits break one of the biggest constraints to practical quantum computers

A proof-of-concept published today in Nature promises warmer, cheaper and more robust quantum computing.

Future quantum computers may pose threat to today's most-secure communications

Quantum computers that are exponentially faster than any of our current classical computers and are capable of code-breaking applications could be available in 12 to 15 years, posing major risks to the security of current communications systems, according to a new RAND Corporation report.

Novel error-correction scheme developed for quantum computers

Experimental quantum computers are plagued with errors. Here Dr Arne Grimsmo from the University of Sydney and colleagues from RMIT and the University of Queensland offer a novel method to reduce errors in a scheme applicable across different types of quantum hardware.

Read More: Quantum Computers News and Quantum Computers Current Events

Brightsurf.com is a participant in the Amazon Services LLC Associates Program, an affiliate advertising program designed to provide a means for sites to earn advertising fees by advertising and linking to Amazon.com.