First Quantum‑Computer Simulation of a Deuteron Nucleus

• Nuclear physicists have, for the first time, simulated an atomic nucleus on a quantum computer.
• The team wrote code that ran on both the Rigetti 19Q and IBM QX5 quantum processors accessed via the cloud.
• These initial results pave the way for quantum‑driven studies of heavier nuclei through remote, cloud‑based quantum resources.

Quantum computing extends beyond speed; it transforms how machines process information. While classical computers use bits that are either 0 or 1, quantum bits (qubits) can exist in a superposition of both states simultaneously, vastly expanding computational possibilities.

Oak Ridge National Laboratory researchers recently demonstrated this power by simulating a deuteron— a stable nucleus made of one proton and one neutron—using cloud‑based quantum processors.

Tools Used

The project began in late 2017 with code designed to run complex nuclear simulations on the Rigetti 19Q and IBM QX5 devices. Employing multiple hardware platforms helped validate the results across different quantum architectures.

The team leveraged the open‑source Python library pyQuil—a tool for writing quantum instruction language programs—to generate hardware‑specific code that was executed on both Rigetti and IBM machines.

What Was Measured?

Using quantum computing, the researchers performed over 700,000 individual measurements to determine the binding (or separation) energy of the deuteron—the minimum energy required to break it into a proton and a neutron.

A deuteron, the bound state of a neutron (blue) and a proton (red). Image credit: Andy Sproles

Choosing the deuteron was strategic: it is the simplest composite nucleus, highly stable, and naturally abundant in seawater, making it an ideal test case for quantum simulation.

Reference: Phys. Rev. Lett. 120, 210501 (2018) | Oak Ridge National Laboratory

Although qubits are not protons or neutrons, the team mapped nuclear properties onto quantum bits to simulate the deuteron’s binding energy. They constructed a deuteron Hamiltonian using pionless effective field theory and employed a variational wave‑function ansatz based on unitary coupled‑cluster theory. By reducing circuit depth, all operations fit within the device’s decoherence time.

Challenges Faced

Running the simulations remotely introduced latency, so each calculation was repeated 8,000 times to ensure statistical reliability.

Quantum processors are notoriously noisy. External perturbations can significantly alter measurement outcomes. To mitigate this, the researchers injected artificial noise and extrapolated results to the zero‑noise limit.

Results and Implications

Two‑qubit simulations on both processors produced consistent results with small uncertainties. When extrapolated to infinite space, the calculated binding energy was within 2% of the known deuteron value.

Adding a third qubit increased complexity due to entanglement errors, but the extrapolated result remained within 3% of the exact value.

These successes demonstrate that quantum computers can accurately model simple nuclear systems and hint at the potential for studying heavier nuclei through cloud‑based quantum access, offering deeper insights into nuclear structure, element formation, and the origins of the universe.