- For the first time, nuclear physicists simulated an atomic nucleus on a quantum computer.
- They developed the code to execute simulation on Rigetti 19Q and IBM QX5 quantum processors.
- The results could open a new door for quantum computation of heavier nuclei via cloud access.
Quantum computing isn’t just about speed – it’s changing the way machines think and work. Unlike digital bits, the units used by quantum computers (qubits) store data in 2-state systems, like protons and electrons, which could remain in multiple quantum states (a phenomenon called superposition) at once.
The conventional computer writes bits in ‘one’ and ‘zero’. However, qubits can have ‘zero’, ‘one’, and any possible combination of both, extending the possibilities of storing information.
Recently, nuclear physicists at Oak Ridge National Laboratory simulated an atomic nucleus using quantum processors (accessed via clouds). This is the first time someone has demonstrated the capabilities of quantum systems for computing nuclear physics problems.
The research team begun developing code in the last quarter of 2017, to execute complex simulation on the Rigetti 19Q and IBM QX5 quantum processors. More than one system is used to verify and validate the simulations on different classes of quantum hardware.
They used an open-source python library pyQuil — developed for writing code in quantum instruction language — to create hardware-specific programs, which were later executed on both Rigetti and IBM quantum computers.
What Did They Measure?
Using quantum computing, the research team measured the energy of a deuteron – a stable particle composed of one neutron and one proton. More specifically, they carried out over 700,000 measurements to find out binding/separation energy of a deuteron – the minimal energy required to disassemble it into subatomic particles.
A deuteron representing the bound state of a neutron (blue) and a proton (red) | Image credit: Andy Sproles
Why deuteron, you asked? Well, it’s nucleus of deuterium, which has a natural abundance in the oceans. And since it’s simplest composite atomic nucleus with remarkable stability, it’s a perfect candidate for the research.
Qubit doesn’t have any properties of proton or neutron. So, scientists mapped these properties to quantum bits, to simulate the binding energy of a deuteron.
They introduced a deuteron Hamiltonian from pionless effective field theory in a way that it can be simulated on a quantum processor. They also developed a variational wave function ansatz based on unitary coupled-cluster theory and decreased the circuit depth so that all operations can be executed within the device’s decoherence time.
The researchers had to execute simulations remotely, and then they had to wait for outcomes, which was one of the major drawbacks of these systems. To ensure values of these outcomes, they executed every single calculation 8000 times.
Since there was a significant amount of inherent noise, it’s quite difficult to work with these quantum systems. If particles comes in and hits the quantum processor, it can change the measurements drastically. To diminish these errors, they added artificial noise and estimated outcomes with zero noise.
Results and Applications
The results of 2-qubit computations on both processors agree with each other with small uncertainties. The extrapolation to infinite space yields a result within 2% of the deuteron’s binding energy.
Implementing 3-qubit makes the measurement quite difficult because of entanglement errors. In this case, the extrapolation to infinite space is within 3% of the exact result.
These results could open a new door for quantum computation of heavier nuclei via cloud access. The researchers believe that the improved quantum machines will enable them to solve more complex problems. It could provide a detailed characteristics of heavier nuclei, the formation of complex elements and origin of the universe.