One of the big challenges for achieving high performing fault tolerant quantum computers is coming up with a way of scaling the number of qubits to the hundreds of thousands or millions of qubits that will be needed to create a usable number of error corrected qubits. Although some approaches, such as quantum dots, may be able to fit a large number of qubits on one chip, they can run into other challenges such as wiring complexity and handling the heat load within the cryostat of the large number of qubits.
So many researchers are looking at ways of implementing these large quantum computers on multiple modules and networking them together to form a larger system. The approach taken by PsiQuantum is a recent example with their proposed system requiring scores of individual modules connected together. Likewise IonQ’s plans for photonics interconnects, or IBM’s modular-centric roadmap to its 1 billion gate Blue Jay system.
Photonic Inc. has taken a novel approach by using a T centre technology which has a carbon-carbon-hydrogen point defect within the tetrahedral silicon unit cell. This is a newer technology but has a lot of potential benefits because it contains spin-photon interface which creates telecom wavelength photons (O-band) that can be easily transmitted over a fiber optic line.
Now, the company has demonstrated the potential of this technology by implementing a teleported C-NOT (tCNOT) between two modules located in separate cryostats connected with 40 meters of fiber optic cable. Although the performance characteristics of this current demonstration was modest, the company projects they will be able to achieve fidelities of 99.8% at an entanglement rate of 197 Khz. If and when such performance is achieved it would open the door to very rapid scaling to to a large error corrected quantum computer. The Photonic approach has a number of potential advantages over other methods. First, their qubits can be mass fabricated as a dense array in silicon. There are no hard constraints about on-chip yield or how many qubits can fit into a fridge. And this approach can provide for all-to-all connectivity which would be ideal for implementing the more efficient Q LDPC codes that researchers are developing. There are other approaches, such as qubit shuttling, that are under investigation for ion trap processors, but these approaches may be substantially slower.
GQI’s Chief Analyst, David Shaw comments that “Photonic has a highly disruptive technology approach. Their silicon spin qubits with optical photonic interconnects also hold out the enticing prospect of synergies in quantum communications and networking. These recent demonstrations are evidence on the way forward. Continued development will enable a wide variety of applications, set a new bar for quantum roadmaps that others will be under pressure to follow, and stand to accelerate the industry.”
Through its existing partnership with Microsoft, Photonic Inc has already lined-up a heavy weight ally to help pull benefits through to customers. But Photonic is not quite alone in pursuing novel methods for quantum networking. Other organizations working on this include MemQ, Nu Quantum, Qunnect, Welinq and MIT.
Additional information about Photonic’s technology and achievement of this milestone can be found in a press release located here, a scientific paper titled Distributed Quantum Computing in Silicon here, a white paper titled Distributed Quantum Computing in Silicon: Entanglement Between Modules here, a recent overview of their T centre technology titled Optical transition parameters of the silicon T centre here, and a blog from Microsoft that discusses their collaboration with Photonic here. In addition, Photonic and Microsoft have produced a nice video that shows how the teleported CNOT is implemented. The video can be seen here. Photonic will also be making presentations about this technology next week at both the IQT Vancouver/Pacific Rim in Vancouver, Canada as well as the Economist’s 3rd annual Commercialising Quantum Global 2024 in London, England.
For more background, please read GQI’s recent Outlook Report: Scalable Quantum Hardware
May 30, 2024