Accessible Photon Emission Could Bring Quantum Computing Out of the Lab

Researchers from the Tyndall National Institute in Cork have created micro-structures shaped like small pyramids that can create entangled photons. Does this mean that quantum computers are closer than we realize?

Eve of Quantum Computing

Quantum computers have been the stuff of science fiction for the past few decades. In recent times, quantum computers have slowly become more of a reality with some machines successfully solving real world problems such as games and path finding algorithms.

But why are quantum computers so desired by tech firms and why is there so much research into the field? Silicon has been incredibly loyal to the tech world for the past 50 years, giving us the point contact transistor in 1947. Now, silicon is at the center of technology with computers, tablets, smartphones, the IoT, and even everyday items. In fact, you cannot walk down a city street without being in range of some Wi-Fi network or influence from a small silicon device.

However, silicon, for all its uses, has started to reach its maximum potential with Moore’s Law starting to fracture. It has been estimated that within the next 10-15 years, transistor count will no longer increase at the expected rate and will eventually level off, attaining some maximum value. When this happens, devices will not become more powerful thanks to transistor increase and this will directly impact how technology advances.

Transistors can only get so small

While there are some methods that can be employed to continue the trend in increasing computer power (such as the use of hardware solutions to increase software speed and more efficiently written code), they can only go so far. Other more exotic methods include the use of computers which are designed in a similar fashion to brains that can adapt to specific problems.

One computer design, however, is particularly sought after as it could increase computational power exponentially. This computational power comes in the form of quantum computing.

Many are mislead into believing that quantum computers will replace classical computing-based devices (i.e., just about every computer ever made)—this is a myth. Quantum computers, if introduced to the public, would work alongside classical devices as they are very good at solving specific problems. For example, a quantum computer could be used to solve encryption algorithms much faster than classical computers but running a program like Word or Chrome would be better done on an Intel i7 instead of a D-Wave quantum computer.

The Challenges of Quantum Computing

Given all of the interest and research into quantum computers, why are they not currently available to the public or even to big businesses and tech companies? The issue comes down to how quantum computers work and their requirements.

Firstly, quantum devices typically require conditions that simply do not exist outside laboratories. For example, such devices rely on superconductors which need to be kept extremely cold (as low as 0.02K). Secondly, materials that express quantum properties such as entanglement and superposition are needed. Attaining such materials has been achieved using many techniques including trapping silicon atoms in diamond to produce quantum emitters.

However, these techniques do not currently provide mass production capabilities, unlike silicon chips which can be made in the billions with relative ease. One research team from the Tyndall National Institute have devised a method for creating structures that can produce entangled photons.

Nanostructure Pyramid Photon Emitters

Using common semiconductor fabrication techniques and easily obtained materials, the team have created small pyramid structures called “dots” that can emit entangled photons in a specific direction. What makes this research critical to quantum computers is the ability to direct the entangled photos while being able to control the emission via an external electrical source.
If classical computers are to interact with quantum computers, the two need to be able to communicate which is why it is imperative that quantum information can be generated using classical methods and then encoded back into electrical current.

Quantum dot LED cross-section. Image courtesy of Roisin Kelly, Tyndall National Institute, University College Cork

The tiny pyramids are made using epitaxial growth (growth of a crystal structure on top of a pre-existing crystal layer), inside an inverted pyramid structure that is patterned using standard lithography on a 111 (crystal orientation) GaAs substrate.

This production technique allows the pyramids to be manufactured by most (if not all) semiconductor manufacturers which is crucial for mass production. It also allows for the devices to be designed on a piece of silicon that could also hold transistors and other components which brings quantum computers a step closer to being a reality.

The quantum LEDs. Image courtesy of Tung-Hsun Chung, Tyndall National Institute, University College Cork

Summary

The big step that these quantum dots represent is that they allow the control and production of particles that can be used for quantum computing and can easily be manufactured with current technology. While the devices on their own cannot process quantum information, they could play a big part in future quantum devices.


Whatever happens, it can be said that quantum power will be needed soon if silicon stagnates in the near future.