Quantum dot qubits picked up two new entries in Nature this week, giving the crowded quantum computing race another reminder that the winner is not settled by qubit count alone. HRL Laboratories reported an 18-qubit silicon spin system with electronic control, Delft University of Technology showed a way to shuttle spin qubits along a tiny on-chip route, and Saxon Q said it is selling diamond-defect machines with more than 100 qubits.
The shared problem is scale. Quantum computers need many reliable qubits plus error correction before they can run complex computations. Some platforms already claim thousands of physical qubits, but smaller systems are still getting attention because their builders argue they may be easier to manufacture, wire, cool, or rearrange.
What are quantum dot qubits?
A quantum dot qubit uses a tiny manufactured trap to hold a single electron, usually in silicon. The electron’s spin can represent a qubit because it can be up, down, or in a quantum combination of both states.
That is attractive because silicon manufacturing is an industrial superpower, not a lab curiosity. The awkward part is control: electron spins are delicate, and many designs use microwave signals, which means more specialized control hardware and more cabling into cryogenic systems.
HRL’s Nature paper describes a different control scheme. Its design uses three quantum dots, each holding one electron, and changes how strongly the electrons interact. Because electron spins are constrained by quantum rules such as the Pauli exclusion principle, tuning those interactions can drive qubit operations without microwave pulses.
HRL also described a cold control system sitting between room temperature and the qubit chip. The controller is a conventional processor designed for low-temperature, low-power use, drawing less than 3.5 watts despite being built on a 130 nm process. Instructions are compiled elsewhere, loaded into the controller, and then run without constant outside intervention. A superconducting ribbon cable links the controller to the qubit chip.
The reported device had 18 qubits. HRL ran a small error-correction code and reported a logical error rate below 1 percent. That does not make it a useful fault-tolerant computer, but it suggests the remaining work may be mostly engineering rather than a dead end in physics.
Why is IBM interested in quantum dot qubits?
IBM has mainly pushed superconducting transmon qubits, which are controlled with microwave pulses. Even so, IBM now owns the HRL-developed work, according to Ars Technica, and IBM director of research Jay Gambetta told Ars that both superconducting and spin-qubit approaches share a silicon base.
Gambetta said that common foundation gives IBM room to develop both lines in parallel. He also suggested future systems could mix roles, with different hardware or error-correction codes optimized for memory or for producing magic states, a resource needed by many fault-tolerant quantum computing schemes.
Delft’s Nature paper attacks a different limitation of manufactured qubits: fixed wiring. If qubits can only talk to neighbors chosen when the chip was laid out, the error-correction code is partly baked into the hardware. Delft’s team showed a 1.2 micrometer electron “bus” with stops where spins can be stored, and reported nearly 98 percent fidelity for moving a spin from one end to the other and back.
The Delft group also ran a small error-correction demonstration and identified two main error sources: noise during spin exchanges used for entanglement, and loss of coherence while qubits move or sit idle.
Saxon Q is taking the spin idea into diamond. Its qubits use nitrogen-vacancy defects, where a nitrogen impurity leaves a neighboring electron whose spin can be controlled. The company, a Universität Leipzig spinout, says it can place those vacancies within a 10-nanometer radius.
Saxon Q says its systems run at room temperature, fit in a standard rack, and plug into ordinary power. It builds eight-qubit cores and says it is selling machines with more than 100 total qubits, with shipments expected within months and larger systems planned next year. The company claims gate fidelity above 99.9 percent, though these machines are still too small for meaningful error-corrected computing.
This story draws on original reporting from Ars Technica.
