Benchmarking a Spin-Based Quantum Computer
The race to build useful quantum computers has been dominated by devices based on superconducting circuits, which now run to thousands of qubits. But other platforms have certain characteristics that make them competitive even if they can’t yet match those numbers. Computers whose qubits are formed by electron spins in semiconductor quantum dots, for example, have an advantage in that they can be built using complementary-metal-oxide-semiconductor (CMOS) techniques that already underlie the mass-production of integrated circuits. Now Irene Fernández de Fuentes at Delft University of Technology in the Netherlands and colleagues have demonstrated a spin-based quantum computer containing six qubits [1]. The experiment identifies some of the challenges that must be overcome to scale up to tens or hundreds of qubits.
The team’s device consists of layers of silicon and silicon-germanium in which a row of six quantum dots is defined by electrodes. Single-electron spins confined in the dots constitute the qubits. Electric fields control the interactions between adjacent spins, while microwave pulses flip the spin qubits’ states. In earlier work, the researchers used this six-qubit processor to characterize processes that involved one, two, or three qubits at a time. In their latest experiment, they implemented a more complex protocol that spreads entanglement across the entire processor via two-qubit operations between all nearest neighbors. To gauge the fidelity of the protocol, they applied a time-reversed version of it and measured how closely the processor returned to its initial state.
The researchers found that the fidelity dropped significantly as the number of qubits and the length of the computation increased. Both factors introduced more noise. Fernández de Fuentes anticipates that this noise could be mitigated in future devices by employing parallel processes and faster operations.
–Marric Stephens
Marric Stephens is a Corresponding Editor for Physics Magazine based in Bristol, UK
References
- I. Fernández de Fuentes et al., “Running a six-qubit quantum circuit on a silicon spin-qubit array,” PRX Quantum 7, 010308 (2026).