Promising Material For High-Speed, Secure Quantum Internet

  • Physicists ‘rediscovered’ a material that could make ultrahigh-speed quantum internet a reality. 
  • It’s silicon carbide (SiC). 
  • It emits photons efficiently, and thus can transfer data at 1 Gbps on quantum cryptography protocols. 

Quantum computing will soon revolutionize the digital machines. For the last couple of years, tech giants like IBM, Microsoft, Google, and leading research centers have been working on quantum machines. We haven’t built a real quantum machine yet, but the tech world is slowly getting ready.

One of the major expectations is that quantum computing will break all the security by decoding all the data encrypted by today’s computers. It could perform extremely complex tasks in seconds that would take a conventional supercomputer years to solve.

Fortunately, quantum technologies come with a solution to neutralize the security-breach threat. The cryptographic algorithms we use today are based on certain complexity, which can be cracked when more powerful hardwares come in the market.

On the other hand, quantum cryptography is based on physics laws, and it guarantees secure transmission of data forever. It works on the principle that no one can copy a secret quantum state without changing its data. Even if eavesdroppers use quantum computer, they can’t read data without the receiver and the sender knowing.

Quantum Data Transmission

So far, photon is the best known carrier for qubits (or quantum bits). To transmit a piece of data, only a single photon can be used, otherwise attackers could intercept one of the photons, extracting a copy of the data.

How these photons are generated, you asked? Well, you need a material that can efficiently and reliably produce photons under specific scenarios. Finding or discovering such a thing is a really tough job.

Quantum dots are fine candidate, but they operate at extremely cold temperature (less than 70 Kelvin). Whereas newly discovered materials like graphene do not produce large amounts of photons under electrical excitation.

Therefore physicists at Moscow Institute of Physics and Technology, Russia, came up with an old material that could make ultrahigh-speed quantum internet a reality. It’s a long forgotten semiconductor material, Silicon carbide (SiC).

Image Credit: Elena Khavina, MIPT

Why Silicon Carbide?

Silicon carbide occurs naturally as a rare mineral moissanite. Its powder has been synthetically produced since 1893 as an abrasive. In fact, it started a whole new optoelectronics era – electroluminescence. 

Its electronic applications, including detectors in early radios and light-emitting diodes (LEDs) were first demonstrated in 1910s. They were mass-produced in 1970s in different countries. However, SiC LEDs were later abandoned because gallium nitride showed up to 100 times brighter emission.

Nowadays, silicon carbide is mostly used in applications requiring high endurance, like ceramic plates in bulletproof vests, breaks and clutches in sports cars manufactured by Lamborghini, Ferrari and Porsche. And, it’s used in electronic devices that operate at high voltages and high temperatures.

At present, color centers (defects in crystal lattice) in diamond are considered as the most promising quantum system for practical sources of light. These color centers can absorb or emit photons at a particular frequency to which the material is transparent when there is no defect.

Reference: Nature | doi:10.1038/s41534-018-0066-2 | MIPT

Researchers analyzed the color centers’ electroluminescence in SiC and theorized a concept of single-photon emission under electric impulse that describes and precisely reproduces the experimental results.

Electron capture process by positively charged color center. r(T) is Thomson radius  

Using this theory, they showed how SiC diode can be enhanced to emit billions of photons per second. This could enable data transfer at the rate of 1 Gigabits per second on quantum cryptography protocols.

They have demonstrated that the rate of photon emission from silicon carbide diode, at room temperature, can reach 5 Gcount per second, which is greater than what can be obtained via epitaxial quantum dots or electrically driven color centers in diamond.

Moreover, theoretical researchers suggest that this emission rate could be further increased to 15 Gcount per second by improving donor doping profile.

Read: A New Form Of Light That Could Make Quantum Computing Possible With Photons

We may find similar material in the future, but, unlike SiC, they will need new techniques for mass production and device integration.

However, photon sources based on SiC are already compatible with CMOS (complementary metal-oxide-semiconductor) technology, which makes SiC by far the most favorable material for developing high-bandwidth lines.

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