Quantum researchers from Trinity College Dublin have successfully modelled an exotic form of particle transport known as superdiffusion on an early quantum processor. This milestone proof-of-concept simulation demonstrates nascent quantum computers’ potential for unravelling complex quantum phenomena beyond conventional machines’ capabilities.

Superdiffusion refers to a type of bizarre diffusion where particles or entities spread in a medium at a rate faster than in normal, or “classical,” diffusion.

The Trinity team, collaborating with IBM researchers in Dublin, realized the simulation on a 27-qubit superconducting quantum processor. By remotely programming the quantum device, they simulated the intricate quantum behaviour of interacting particles displaying superdiffusion.

The project provides a glimpse into future quantum advantage for gleaning insights into frontier physics and materials science. As hardware scales up in coming years, quantum computers promise to reshape research into quantum matter’s enigmatic workings.

## Quantum Simulation Circumvents Classical Limits

Quantum systems present knotty challenges to simulate using regular computers. Representing the full quantum state of multi-particle systems requires memory to grow exponentially with particle count. Even modelling just hundreds of quantum constituents soon overwhelms classical capabilities.

Quantum computers hold innate advantages for simulating quantum systems by exploiting their quantum nature. Their discrete quantum bits or qubits exist in a shared quantum state described by a wavefunction. This avoids the exponential storage needed classically to depict each probable state.

In the words of Trinity quantum physicist Professor John Goold, “You naturally exploit the fact that the quantum computer is described by a wavefunction thus circumventing the need for exponential classical resources.” This makes quantum platforms ideal for probing quantum phenomena like superdiffusion intractable otherwise.

## Investigating Superdiffusion in a Quantum Spin Chain

The Trinity/IBM collaboration focused on examining transport dynamics in a Heisenberg quantum spin chain – a line of interconnected subatomic magnets modelling more complex quantum materials. Spin chains provide fertile testing grounds for illuminating mysteries of quantum behaviour.

Specifically, the researchers aimed to simulate an intriguing form of spin transport called superdiffusion. In certain regimes, excitations can propagate faster through quantum spin systems as their size increases. This resembles classical superdiffusion processes like ink spreading rapidly through paper.

Observing this curious conduct required modelling the spin chain’s long-term evolution. As time progressed, the system entered a hydrodynamic state where quantum particles flowed akin to classical fluids. The team successfully simulated this complex many-body behaviour on the quantum hardware.

## Quantum Platform Programming Challenges

The project provided invaluable hands-on experience tailoring algorithms to noisy intermediate-scale quantum (NISQ) devices. IBM-Trinity scholar Nathan Keenan, who coded the quantum simulation, explains that error mitigation is critical when programming early quantum computers.

The imperfect low-level operations and interference from the environment mandate short, efficient programs before noise accumulates. This requires creatively mapping problems into compact circuits tolerating some errors while maintaining valid output. Developing such programming techniques will be essential as quantum computing moves toward practicality.

## Early Quantum Computers Complement Classical Techniques

While universal quantum computing remains years away, current NISQ systems offer a platform for trailblazing quantum simulations inaccessible otherwise. Hybrid algorithms pairing quantum circuits with classical computing also boost capabilities.

IBM, which contributed key hardware and expertise to the project, has pioneered commercial quantum computing efforts for over two decades. Juan Bernabé-Moreno of IBM Research UK and Ireland says collaborations with institutions like Trinity provide invaluable hands-on training while delivering promising early results.

Quantum cross-pollination between academia and industry accelerates translating futuristic technologies into real-world impact. As quantum hardware and software continue rapidly developing in tandem, a new era of quantum-enhanced simulation nears.

## Harnessing Quantum Advantage for Breakthrough Science

Quantum simulation promises game-changing advantages across scientific domains like chemistry, physics, materials science, and more. Trinity’s undertaking, led by pioneering quantum physicist Professor John Goold, provides an exciting signal of this emerging simulation power.

The demonstrated superdiffusion model is but a small glimpse of the exotic quantum phenomena quantum computers may soon elucidate. Within the decade, researchers anticipate profound insights into quantum matter and dynamics beyond current understanding.

Ireland’s position at the bleeding edge also signals its ascent as a quantum hub. Trinity’s newly launched Quantum Alliance pools industrial collaborators like IBM alongside government and academic partners to drive Irish innovations. The quantum future appears bright on the Emerald Isle.

Read More: “Evidence of Kardar-Parisi-Zhang scaling on a digital quantum simulator” by Nathan Keenan, Niall F. Robertson, Tara Murphy, Sergiy Zhuk and John Goold, 20 July 2023, *npj Quantum Information*.

DOI: 10.1038/s41534-023-00742-4