The end of the year is nearing, and quantum computer announcements typically flood in around this time of year, in part because some companies want to keep to their promised schedules. Most of these include evolutionary improvements to previous generations of hardware. But this year, we are the first company to bring new qubit technology to market.
The technology, called dual-rail qubits, aims to make error correction much more efficient by making it easier for hardware to detect the most common forms of errors. And while tech giant Amazon is experimenting with them, a startup called Quantum Circuits is providing public access to dual-rail qubits for the first time via a cloud service.
This technology is interesting in itself, but it also provides insight into how the field as a whole is thinking about making error-correcting quantum computing work.
What is a dual-rail qubit?
Dual-rail qubits are a variant of the hardware used in transmons and are the qubits preferred by companies like Google and IBM. The basic hardware unit links loops of superconducting wire to small cavities that allow microwave photons to resonate. This setup allows the presence of microwave photons in the resonator to influence the behavior of the current in the wire, and vice versa. In transmon, microwave photons are used to control the electrical current. But other companies are developing hardware that does the opposite, controlling the state of photons by changing the electrical current.
Dual-rail qubits use two of these systems linked together, allowing photons to travel from one resonator to the other. Using superconducting loops, we can control the probability that a photon will reach the left or right resonator. The photon’s actual position remains unknown until it is measured, allowing the entire system to hold a single bit of quantum information, or qubit.
