Solving Quantum Challenges with Photonic Quantum Chips

May 15, 2021 by Kristijan Nelkovski

Though research on quantum computing is booming, there are still many real-world challenges to overcome, though photonic quantum chips might help.

For today’s quantum computers to function properly, it’s necessary to isolate them from environmental noise and reduce possible errors to delay quantum decoherence and achieve viable calculations. To isolate them requires a large cooling, wiring, and shielding infrastructure even when using a small number of qubits.


A diagram of a photonic qubit conversion from one frequency to another.

A diagram of a photonic qubit conversion from one frequency to another. Image used courtesy of Philipp Treutlein

Companies are testing other natural phenomena searching for more stable technologies that could lead to practical quantum processor designs to overcome these problems. 

Photonics is one promising alternative as photons can represent qubits and are less environmentally affected than other particles.


Developing a Million-qubit Quantum Computer

Towards innovating quantum computing, Palo Alto’s PsiQuantum is a four-year-old photonic quantum computing company that has raised millions through funding and has recently reached manufacturing milestones with GlobalFoundries. 

The CEO, Jeremy O’Brien states that their goal is to create a commercial quantum computing system containing a minimum of one million qubits suggesting that his company would build it within a handful of years. 


Testing the PsiQuantum silicon wafer.

Testing the PsiQuantum silicon wafer. Image used courtesy of PsiQuantum


Terry Rudolph, the co-founder, and grandson of Erwin Schrödinger, add that their technology is important because, in contrast with other particles, their photons do not decohere and do not interact with each other eliminating many timing and crosstalk errors present in other designs. He explains that their fault-tolerant architecture is not an added-on feature but an intrinsic part of its design. 

PsiQuantum’s qubits are encoded using single photons traveling along silicon photonic waveguides and are entangled using networks of optical components on a semiconductor photonic chip-based system. According to Rudolph, semiconductor fabs such as PsiQuamtum’s supplier, GlobalFoundries, already produce chips with billions of transistors for phones and computers and should be able to handle chips with millions of qubits as well.

Even with research towards a quantum computer, there still needs to be a focus on one of the biggest challenges of any electronic device: temperature.


Room-temperature Quantum Computing

Canadian-based Xanadu, also founded four years ago, is another company working in photonic quantum computing.


A computer-generated representation of Xanadu’s X8 chip.

A computer-generated representation of Xanadu’s X8 chip. Image used courtesy of Xanadu


Xanadu's X8 chip, which contains eight squeezed quantum states, is silicon-based, much like PsiQuantum’s tech, and is compatible with current semiconductor fabrication methods based on nanophotonic silicon nitride waveguides. 

Interestingly, Xanadu’s technology is that most of its hardware operates at room temperature, excluding photon-counting detectors responsible for reading the quantum states of entangled photons. The company’s CEO Christian Weedbrook states that they are currently testing different types of sensors and are well on their way to a fully room-temperature quantum computer giving a similar ‘couple of years’ timeframe as PsiQuantum. 

Xanadu also offers a cloud platform like IBM Quantum and Microsoft’s Azure. However, it is the first of its kind being a photonic quantum computing cloud platform. According to Weedbrook, the company has customers paying for cloud time, and physicists and engineers are already excitedly experimenting and testing out a real quantum chip.


Implications of Developing Photonic Quantum Chips

PsiQuantum and Xanadu's designs are essential because their designs rely on already proven semiconductor manufacturing techniques, ensuring an easier transition into quantum computing for EE engineers in both use and manufacturing, allowing for rapid testing and easier development. 

Although scaling the technology is a challenge, physicists and engineers might have a winning combination of intersecting photonics and classical semiconductor fabrication with quantum computing. This interdisciplinary research can eliminate temperature and entanglement problems and bring the number of qubits to a more manageable level to solve complex real-world engineering challenges instead of carefully crafted mathematical problems. 

However, whether or not these companies achieve their goal and bring stable, room temperature photonic quantum computers to the world market remains a question of time, ingenuity, and any possible limitations presented by the laws of quantum mechanics.