Quantum computing breakthrough has atoms 'chatting' long distance inside silicon chips

Quantum computing needs qubits that can work together without getting scrambled by noise. Engineers in Sydney have demonstrated a clean way to entangle nuclear spins inside silicon chips.

They persuaded two atomic nuclei to share a quantum link even though the atoms were not in the same place. The key move was to let nearby electrons carry information between them.

Nuclear spin and silicon chips

Lead author Dr. Holly Stemp at the University of New South Wales (UNSW), now a postdoctoral researcher at MIT, led the team that built and tested the device.

The work sits inside a silicon chip, not a lab-only contraption.

“We succeeded in making the cleanest, most isolated quantum objects talk to each other, at the scale at which standard silicon electronic devices are currently fabricated,” said Stemp.

This approach lines up with how modern chips are already made. It does not need exotic materials or one-off fabrication tricks.

The result targets a long standing bottleneck. Qubits must be quiet enough to hold information, yet still able to interact when we need them to compute.

What changed in this experiment

The team realized a geometric controlled Z operation that entangles two phosphorus nuclear spins across about 20 nanometers, completing in roughly 2 microseconds. That distance is similar to features used in mainstream chipmaking.

Entanglement means two quantum systems become linked so that a measurement of one immediately tells you something about the other. The pair no longer behaves as independent parts.

A qubit is the quantum version of a bit, and a nuclear qubit uses the nuclear spin of an atom as its information carrier. Phosphorus donors in silicon provide a stable way to host that spin.

Earlier nuclear spin devices needed both nuclei to share the same electron to talk. Here, each nucleus keeps its own electron, and the electrons interact with one another through the exchange interaction controlled by gate voltages.

Entanglement and quantum computing

The exchange interaction couples the two electrons even when the atomic nuclei are not neighbors. By tuning that coupling, the device lets electrons mediate a precise, switchable link between distant nuclei.

Microwave pulses set by electron spin resonance select which electron transition happens, and that transition depends on the states of both nuclei.

In this way, the electrons act as controllable messengers between nuclear qubits.

A controlled Z gate flips a quantum phase only when a chosen control qubit sits in a particular state.

In this device the gate is geometric, so the phase comes from the path the electron spin takes under control, and the operation finishes in about 2 microseconds.

“With this breakthrough, it’s as if we gave people telephones to communicate to other rooms,” said Stemp.

Why nuclear spins still matter

Nuclear spins are famously quiet. Ensemble experiments in isotopically purified silicon reached a room temperature coherence time of about 39 minutes.

Single donor devices have already shown high fidelity readout and coherent control of a phosphorus nuclear spin qubit in silicon.

Those results established that nuclear spins can hit the accuracy targets needed for useful computation.

Silicon adds a practical benefit. The material already underpins most electronics, so building quantum parts in silicon can reuse tools and processes that industry knows well.

From vision to silicon reality

The idea of a silicon quantum computer driven by donor nuclear spins goes back more than two decades. Bruce Kane from the University of New South Wales outlined that proposal to place phosphorus atoms in silicon and use their nuclear spins as qubits.

Electrical control of two qubit logic with exchange has also worked with electron spins in silicon quantum dots. That study showed how exchanges can drive fast, controllable two-qubit gates in a silicon platform.

The new work connects these threads by letting electrons do the coupling while the nuclei store information. It keeps the memory quiet and the interactions fast.

What quantum computing means for chips

Silicon donor devices already talk the language of metal oxide semiconductor processing. That means more qubits can be added without reinventing the factory floor.

Electrons can be moved and shaped by voltages, which turns the interactions on and off in a programmable way. That will matter for routing connections among many qubits without adding noise.

This strategy avoids crowding multiple nuclei around one electron. Each nucleus keeps a clean local environment, while electrons reach across to build the needed links.

Scaling will still demand improvements in initialization and control to keep errors low. Yet the path forward looks compatible with the same tools used to push classical chips to billions of devices.

The study is published in Science.

—–

Like what you read? Subscribe to our newsletter for engaging articles, exclusive content, and the latest updates. 

Check us out on EarthSnap, a free app brought to you by Eric Ralls and Earth.com.

—–