Most efforts to build a quantum computer rely on exotic hardware cooled to temperatures colder than outer space, but two well-funded startups are betting that light itself holds the key, using individual particles of light called photons to perform calculations that would overwhelm even the most powerful conventional machines.
Xanadu, a Toronto-based company that listed on the Nasdaq and Toronto Stock Exchange last month at a valuation of roughly $3.6 billion, and PsiQuantum, a privately held Silicon Valley firm valued at approximately $7 billion, are both presenting detailed roadmaps for how they intend to scale photonic quantum computers to a size where they become genuinely useful.
The two companies agree on the basic premise: photons can carry quantum information, they travel naturally through the same optical fibre that already underpins the internet, and the chips that manipulate them can be manufactured using existing semiconductor factory processes, potentially making them far cheaper and easier to produce at scale than competing designs.
Beyond that, they diverge sharply.
Xanadu encodes information not in individual photons but in the broader light field surrounding them, using a technique called squeezing that reduces uncertainty in one property of the light at the cost of increasing it in another.
The company has demonstrated a series of progressively more complex machines, most recently a modular system called Aurora that linked 12 logical qubits, the basic units of quantum information, across 35 chips connected by more than 13 kilometres of optical fibre.
Xanadu's long-term target is up to 1,000 logical qubits, which at the roughly 100-to-one ratio of physical components needed to protect each logical qubit from errors would require around 100,000 physical qubits.
PsiQuantum takes a different path, encoding information in the presence or absence of a single photon travelling down one of two possible routes on a chip.
The approach is conceptually simpler but demands extraordinary precision, because when a single photon is lost there is no way to recover the information it carried, a consequence of a rule in quantum physics that forbids copying quantum states.
PsiQuantum has focused heavily on manufacturing partnerships, working with GlobalFoundries, a major chipmaker, to produce its components at the volumes needed for machines containing a million or more physical qubits.
Both approaches face significant engineering hurdles.
Photons are easily lost as they travel through a chip or along a fibre, and reducing that loss rate is one of the central challenges for the entire field.
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Xanadu has reported a 60% reduction in optical losses and is working with specialist partners to improve further, while PsiQuantum published research in the journal Nature documenting its manufacturing platform and test results.
The stakes extend well beyond the two companies, because a working large-scale quantum computer could transform drug discovery, materials science and cryptography, while also threatening the encryption that protects financial systems and government communications.
The recap
- Two companies detail hardware roadmaps for photonic quantum computing.
- PsiQuantum holds an estimated $7 billion valuation after Series E funding.
- Xanadu targets up to 1,000 logical qubits by 2029 using GKP.
