The discovery of quantum computers and photonics can reduce the complexity of the parameters by 1,000 times

Researchers have discovered a potential miniaturization of quantum computing, which could reduce resources by 1,000 times while requiring less hardware. This research is published in Nature Photonics.

A class of quantum computers currently being developed relies on particles, or photons, made up of entangled pairs or “bound” in quantum physics parlance. One way to create these photons is to shine a laser on millimeter-thick crystals and use detectors to make sure the photons collide. A limitation of this method is that it is too large to be integrated into a computer chip.

Now, scientists at Nanyang Technological University, Singapore (NTU Singapore) have found a solution to this problem by creating coherent photons using ultra-thin materials that are only 1.2 micrometers thick, or about 80 times thinner than a hair. And they did this without needing additional optical equipment to maintain the link between the photon pairs, making the whole setup simpler.

“Our new technique for creating entangled photon pairs opens the way to miniaturizing quantum optical entanglement sources, which will be important for applications in information technology and photonic quantum computing,” said Prof Gao Weibo of NTU, who led the research.

He added that this method could reduce the size of quantum devices because most of these devices currently require large and bulky devices, which are difficult to connect, before they can start working.

Thinners

Quantum computers are expected to revolutionize the way we tackle many problems, from helping us better understand climate change to finding new drugs faster by completing complex calculations and quickly finding patterns on large data sets. For example, calculations that would take today’s supercomputers millions of years to solve can be done in a matter of minutes with quantum computers.

This is expected to happen because quantum computers perform many calculations at once instead of one at a time like conventional computers.

Quantum computers can do so when they calculate using tiny switches called quantum bits, or qubits, that can be turned on and off at the same time. It’s like flipping a coin upside down, the coin that spins is between heads and tails. In contrast, conventional computers use switches that can be turned on or off at any time, but not all.

Images can be used as qubits so that computers can be scaled up to perform calculations as fast as they can and stop at the same time. But being in two states at once only happens when the photons are created in pairs, with one photon attached, or locked, to the other. The key to binding is that the entangled photons must vibrate when interacting.

One advantage of using photons as qubits is that they can be produced and trapped at room temperature. Relying on photons would be simpler, cheaper and more efficient than using particles such as electrons that need to be superheated near the freezing point of space before they can be used for quantum computing.

Researchers have been trying to find ultra-thin materials to make coherent photons that can be used in computer chips. However, another problem is that when matter shrinks, it emits photons at a very low rate, which is impossible to use with computers.

Recent progress has shown that a promising new crystalline material called niobium oxide dichloride, which has unique optical and electrical properties, can efficiently produce two photons despite its thinness. But these two photons are useless in quantum computers because they are not bound when they are created.

The answer was found by NTU scientists led by Prof Gao, from the University’s School of Electrical & Electronic Engineering and School of Physical & Mathematical Sciences, in collaboration with Prof Liu Zheng from the School of Materials Science & Engineering.

Obsession with tradition

Prof. Gao’s answer was inspired by the established method of creating photon binding with larger and larger crystalline materials, which was published in 1999. It involves placing two flakes of dense crystals together and placing the crystalline grains of each flake perpendicularly to each other.

However, the vibration of the photons produced in the doublet may be non-uniform due to the way they travel inside the dense crystal after it has been formed. Additional materials are needed to combine the photon pairs to maintain the coherence between the light particles.

Professor Gao said that the two parallel crystal systems can be used with two thin crystal flakes of niobium oxide dichloride, with a thickness of 1.2 micrometers, to produce coherent photons without the need for additional equipment.

They expect this to happen because the flakes used are much thinner than the bulkier crystals from earlier studies. As a result, the photon pairs produced travel a short distance within the niobium oxide dichloride flakes, so that the particles are aligned. Experiments with the NTU Singapore team proved his theory correct.

Professor Sun Zhipei of Aalto University in Finland, who works in photography and was not involved in the NTU research, said that trapped photons are like synchronized clocks that show the same time no matter how far apart they are and can communicate instantly.

He added that the NTU team’s method of producing quantum photons “is a major advance, which will enable the miniaturization and integration of quantum technology.”

“This development can improve quantum computing and secure communication, as it allows for more efficient, flexible and efficient methods,” said Prof Sun, co-principal researcher at the Research Council of Finland’s Center of Excellence in Quantum Technology.

The NTU team plans to further develop their design to produce more coherent photons than is currently possible.

Other ideas include investigating whether introducing particles and lines on the surface of niobium oxide dichloride flakes would increase the number of photon pairs produced. One will see if mixing flakes of niobium oxide dichloride with other materials can enhance the production of photons.