New Multi-Colored Photons Could Dramatically Increase Computing Speeds

As the electronics industry continues to follow Moore’s law and computer parts approach the size of an atom, physics starts to get funky.

According to a new study released today, it could get even funkier than we thought.

A team of scientists has made it easier to produce a new unit of measurement in quantum computing, which enables them to encode more information in photons and thus process data more quickly. Their work, which builds on the fundamental principles of quantum mechanics, has the potential to dramatically increase computing speeds.

Photograph of a chip designed to support a 128-qubit processor.

The simplest computational data processors, called transistors, act as physical switches for electrons. They allow bits (pieces of information) set to 0 or 1 to pass through when the switch is open. By continuing to shrink the size of transistors, scientists are approaching a fundamental physical limit where electrons are actually able to pass through a closed switch—a process called quantum tunneling. This quantum phenomenon interferes with how transistors function, but by leveraging other quantum properties, scientists have been able to explore the new world of quantum computing.

And that’s great news, because computing in the quantum realm theoretically offers much more efficient computing than traditional methods. For now, though, the efficiency is limited by the amount of information that quantum devices can process, which has yet to surpass that of traditional computers.

The central principle of quantum mechanics is that, in contrast to classical physics, two states (in computing, 0 and 1) can coexist simultaneously—a concept known as superposition. While in traditional computing, the main unit is a bit, in quantum computing, the primary unit is a qubit that has two dimensions (i.e. 0 and 1 at once).  Wavelengths of light can also represent qubit dimensions, where a photon could possess red and yellow light at once. In a paper released today in Nature, Michael Kues and a team of researchers discussed the next possible unit for quantum computing. They focused on qudits, which are even higher dimensional states, like red and yellow and green and blue light maintained at once, where each color represents a dimension.

As a step towards a practical quantum computer, Kues and his colleagues combined standard optical parts—some of which are used in common telecommunications systems— that are commercially available. One primary component was a ring resonator—a circular piece that traps light much in the way that a whispering gallery traps sound waves. In these galleries, if you stood on one side, a friend on the opposite side of the ring could hear your message very distinctly. Just as sound waves can travel around the gallery of St. Paul’s Cathedral, light can travel around the concave surface of the ring resonator. As the light circles through the ring, some wavelengths of light get reinforced, building in intensity to achieve resonance.

St. Paul's Cathedral hosts one of the first known whispering galleries, with unique acoustic properties.

The scientists achieved multiple colors at once because wavelengths of light can interact and produce new wavelengths of light through a phenomenon known as “spontaneous four-wave mixing.” While in standard telecom, like radio, this can be a problem since producing a new frequency station can diminish audio quality, for quantum optics this produces color-entangled qudits (those higher dimensional alternatives to the qubit). By encoding multiple colors at once, this increases the amount of information each photon can contain.

Since the team did not custom-build their parts, the platform can easily be made by others, which is unusual for quantum computing projects that often require complex, expensive equipment. By using standard optical parts, the team can build on knowledge from telecommunications to make devices, extending the use of traditional telecom parts beyond classical physics. Using integrated platforms like this one allows researchers to create cheaper, smaller quantum devices.

Kues and his colleagues found that their platform can support at least 100 dimensions, but could theoretically support up to 13 qubits, equivalent to over 9,000 dimensions. By increasing the complexity of quantum circuits through higher dimensionality, the researchers are essentially able to provide more information per photon. To be practically useful, though, quantum devices will need to achieve hundreds of qubits, or move to units like qudits.

Achieving these high-dimensional superposition states allows physicists to deeply explore the basic principles of quantum mechanics, but it could also lead to much faster computing. High-dimensionality basically means that you can do lots more (quantum) operations, in parallel, at once, by acting on a single qudit as opposed to doing the same operation on multiple qubits in serial.

To outperform normal computers, quantum computers need to process significantly more information than they presently can. Quantum computing may not be a replacement for our traditional computing needs, but it can outperform alternatives for resource-intense processes.  Database searches, complex simulations, and bioinformatics could benefit from exponential increases in speed this new technology offers. We still do not know if quantum computing will gain mass appeal or remain a specialized tool, but for now we are getting closer to achieving practical quantum computers.