PsiQuantum Raises $150 Million for Quantum Computer Platform

Low-key quantum computing start-up PsiQuantum, recently received $150 million in a Series C funding round that closed earlier this year. European venture capital firm Atomico led the funding, with participation from, among others, Founders Fund, Blackrock, Redpoint Ventures, Ballie Gifford, and Microsoft’s M12 Ventures. With this latest funding, PsiQuantum has raised a total of $215 million since it was founded in Palo Alto, California in 2016.

PsiQuantum’s co-founder, former University of Bristol professor Jeremy O’Brien, has stated that the company plans to build a fault-tolerant quantum computer with one million qubits within five years. According to O’Brien, such a large number of qubits is necessary for effective error correction.

Platform Based on Silicon Photonics Instead of adopting a more common platform, such as superconducting Noisy Intermediate-Scale Quantum or ion trap technologies, PsiQuantum’s system will utilize silicon photonics, which will use photons to perform quantum calculations. Yet based on the company’s patent portfolio, superconductor technology will have a role as well.

A photon could be vertically polarized to represent a one, horizontally polarized as a zero, or diagonally polarized to represent a superposition of both one and zero. They would be sent down pathways placed on a silicon chip.

Miniature, partially reflective mirrors would bounce the photons into a state of entanglement where additional quantum forces could be applied to bind qubits in ways that amplify their forces. Then a sensor would measure the photons and, after additional steps, the PsiQuantum team could produce and read a calculation.

Photon Qubits Have Advantages and Challenges

“Rather than take a quantum system and try to make it scalable, we have taken a scalable process — silicon manufacturing — and made it quantum,” proclaims a blog post on PsiQuantum’s website. “Photonic qubits are inherently low noise and do not interact in uncontrolled ways. They can operate at higher temperatures, which means we can place more control electronics on a quantum chip, improving system integration.

“Modularity and networking are critical elements of scalable error correction. We achieve both, through the manufacturability of our system, and because we can readily send qubits between chips using conventional optical fiber.
“Matter-based approaches need complicated devices to convert qubits into photons to connect modules. Our approach cuts out the middleman; our qubits are always photons.”

Photon qubits would also have the advantage of maintaining their quantum states for a long time. They would be very small, with a wavelength of about 1.0 μm. Yet trying to read, control, and manipulate a million fast-moving photon qubits presents a difficult challenge.

Superconductors Likely to Detect and Read Photons

PsiQuantum is already producing early versions of its chips at Santa Clara, California-based GlobalFoundries. The company has noted that its chips can be produced in standard semiconductor foundries.

Although PsiQuantum has had little problem raising capital, it has been difficult for non-investors to evaluate the efficacy of its technology. The secretive company declines to publish academic papers that can be reviewed for their merits.

When contacted with questions from Superconductor Week, a PsiQuantum spokesperson responded: “I'm afraid at this stage we won't be providing detailed answers to your questions. Having spoken to Bloomberg earlier this year, we're now back to focusing on day to day system development and the engineering challenges associated with that. We will likely release some more detailed technical papers in the future that provide more detail on our approaches and technical choices.”

Although PsiQuantum is not using superconducting technology for its qubits, it appears that it plans to use superconducting devices for photon detection and readout. Since February 2019, the company has been granted ten U.S. patents related to superconductors. These include patents for a niobium-germanium superconducting photon detector, superconducting logic circuits, superconducting logic components, a gated superconducting photon detector, a superconducting signal amplifier, diode devices based on superconductivity, a photodetector with superconductor nanowire transistor based on interlayer heat transfer (see Patents, this issue), superconductor-to-insulator devices (see Patents, this issue), a superconductor-based transistor (see Patents, this issue), and a superconducting photon detector.

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