Discovery of quantum computing and photonics potentially reduces the size of critical parts by 1,000 times

Researchers have made a discovery that could make quantum computing more compact, potentially reducing critical components by 1,000 times while requiring less equipment. The research is published in Natural photonics.

A class of quantum computers under development now relies on light particles, or photons, created in linked pairs, or “entangled” in the language of quantum physics. One way to produce these photons is to shine a laser onto millimeter-thick crystals and use optical equipment to ensure the photons bind. A drawback of this approach is that it is too large to be integrated into a computer chip.

Now, scientists at Nanyang Technological University in Singapore (NTU Singapore) have found a way to solve the problem with this approach by producing bonded pairs of photons using much thinner materials, of a thickness of only 1.2 micrometers, approximately 80 times thinner than a strand of hair. And they did it without needing additional optical equipment to maintain the link between pairs of photons, simplifying the overall setup.

“Our new method for creating entangled photon pairs paves the way for creating much smaller quantum optical entanglement sources, which will be essential for applications in quantum information and photonic quantum computing ” said Professor Gao Weibo of NTU, who led the researchers.

He added that the method could reduce the size of devices for quantum applications, as many of these devices currently require large and bulky optical equipment, which is difficult to align, before they can operate.

Thinner materials

Quantum computers are expected to revolutionize the approach to many challenges, from helping us better understand climate change to finding new drugs more quickly by performing complex calculations and quickly finding patterns in large ensembles of data. For example, calculations that would take supercomputers millions of years today could be performed in minutes by quantum computers.

This should happen because quantum computers perform many calculations simultaneously instead of performing them one by one like standard computers.

Quantum computers can do this by performing calculations using tiny switches called quantum bits, or qubits, which can be turned on and off simultaneously. This is similar to tossing a coin in the air, with the coin spinning in a state between heads and tails. In contrast, standard computers use switches that can be turned on or off at any time, but not both.

Photons can be used as qubits for quantum computers to perform faster calculations because they can have on and off states at the same time. But being in two states simultaneously only happens if the photons are produced in pairs, with one photon bound or entangled with the other. An important condition for entanglement is that the paired photons must vibrate in synchrony.

One of the advantages of using photons as qubits is that they can be produced and entangled at room temperature. Relying on photons may therefore be easier, cheaper and more practical than using other particles like electrons which need ultra-low temperatures close to the cold of space before they can be used for l. quantum computing.

Researchers have been trying to find thinner materials to produce bonded pairs of photons so they can be integrated into computer chips. However, one of the challenges is that as materials become thinner, they produce photons at a much lower rate, which is not practical for computing.

Recent advances have shown that a promising new crystalline material called niobium oxide dichloride, which has unique optical and electronic properties, can efficiently produce photon pairs despite its thinness. But these pairs of photons are useless for quantum computers because they are not entangled when they are produced.

A solution was found by NTU scientists led by Professor Gao, from the university’s School of Electrical and Electronic Engineering and School of Physical and Mathematical Sciences, in collaboration with Professor Liu Zheng from the school of materials science and engineering.

Driven by tradition

Professor Gao’s solution draws on an established method for creating entangled photon pairs with thicker, bulkier crystal materials, published in 1999. It involves stacking two thick crystal flakes and positioning the crystal grains of each flake perpendicular to each other.

However, the vibrations of photons produced in a pair can still be out of sync because of the way they move through thick crystals after they are created. Additional optical equipment is therefore needed to synchronize photon pairs to maintain the link between the light particles.

Professor Gao hypothesized that a similar two-crystal configuration could be used with two thin flakes of niobium oxide dichloride crystal, with a combined thickness of 1.2 micrometers, to produce the bound photons without require additional optical instruments.

He expected this to happen because the flakes used are much finer than the larger crystals from previous studies. As a result, the pairs of photons produced travel a smaller distance in the niobium oxide dichloride flakes, so the light particles remain synchronized with each other. Experiments carried out by the NTU Singapore team proved that their hunch was correct.

Professor Sun Zhipei of Aalto University in Finland, who specializes in photonics and was not involved in NTU’s research, said entangled photons are like synchronized clocks that tell the same time regardless of their distance and can thus enable instant communication.

He added that the NTU team’s method for generating entangled quantum photons “is a major advance, potentially enabling the miniaturization and integration of quantum technologies.”

“This development has the potential to advance quantum computing and secure communication, as it enables more compact, scalable and efficient quantum systems,” said Professor Sun, co-principal investigator at the Center of Excellence in quantum technology from the Research Council of Finland.

The NTU team plans to further optimize the design of their setup to generate even more bonded photon pairs than is currently possible.

Some ideas include exploring whether introducing tiny patterns and grooves to the surface of niobium oxide dichloride flakes can increase the number of photon pairs produced. Another will examine whether stacking niobium oxide dichloride flakes with other materials can stimulate photon production.