NVision, Ulm University unveil light-read molecular qubit

Researchers at the German startup NVision Quantum Technologies and Ulm University have designed a molecule that can work as a quantum bit, or qubit, and be read out individually with light. Chemistry World describes it as the first molecule of its kind to serve as a qubit connected individually by light. The work appeared in Nature on October 28, and NVision now plans to put the molecules onto photonic chips. The goal is to show that molecular qubits, long behind trapped ions, superconducting circuits and neutral atoms, can be made in large numbers.chemistryworld.com

A molecule built for the job

The molecule, di([1,1′-biphenyl]-4-yl)carbene, has four properties an individually addressable qubit needs. Under laser light it fluoresces in only one of its three electron spin states. Those spin states last long enough for computation. It glows brightly enough to be read, and its color holds steady enough to allow entanglement, Chemistry World reported. Until now, scientists could only read molecular qubits in groups and average their values.chemistryworld.com

NVision said it screened more than 150 candidate molecules on computers and made 40 of them in the lab. The team placed a stable precursor inside a crystal made of a nearly identical molecule, cooled it to 4.5 Kelvin, and used a laser to turn the precursor into active qubits. By applying microwave pulses, the researchers extended coherence, a measure of how long the qubit keeps its quantum state, to 2.2 milliseconds. They also found that the molecules' emission frequencies barely moved during more than an hour of repeated excitation.quantumcomputingreport.com+2

Outside experts weigh in

David Awschalom of the University of Chicago called it a "high-quality molecular qubit architecture" and "a significant step towards integrating molecular qubits with scalable optical communication platforms." Danna Freedman of MIT called the demonstration of single-molecule addressability "a huge step for the field".chemistryworld.com

From crystal to chip

NVision wants to use the molecules in an architecture it calls photonic integrated quantum circuits. In this design, electron spins connect to other qubits through light, and nuclear spins act as long-lived memory. The company has partnered with HyperLight, which makes thin-film lithium niobate photonics, and expects its first prototype integrated chips in the fourth quarter of 2026. Its longer-term targets are 1,000 physical qubits and then, by 2030, 1,000 fault-tolerant logical qubits on a chip.optica-opn.org+2

"One of the biggest questions that every modality now faces is: can it scale to hundreds of thousands of qubits?" said Ilai Schwartz, NVision's chief technology officer. "Real engineering challenges remain but because we build on existing foundry processes we don't need to build new factories to get there".chemistryworld.com