Simulating Quantum Particles on a Lattice

Tuesday, September 7, 2021

A team of researchers at the Institute for Quantum Computing (IQC) have developed a new quantum simulator that uses microwave photons in a superconducting cavity to simulate particles on a lattice similar to those found in superconductors or atomic nuclei.

“There is a particular interest in performing quantum simulations of systems that cannot be simulated using even the most powerful classical supercomputers,” said Christopher Wilson, a faculty member at IQC and the Department of Electrical and Computer Engineering at the University of Waterloo.  “While very powerful classical simulation tools exist, many important problems remain intractable.  Here, we present a programmable platform using superconducting quantum circuits. We use it for a small-scale simulation of the bosonic Creutz ladder, an important historical model which exhibits a wide range of interesting behavior including topological and edge states.”

A quantum simulator is a limited-use quantum computer: a machine that can be programmed to replicate the behavior of a specific quantum system that is too complex to simulate using classical methods. Because of their comparative simplicity, many researchers believe that quantum simulators could deliver useful applications sooner than universal quantum computers will. With this goal in mind, Wilson along with his colleagues have used a chip-based superconducting cavity to build a quantum simulator that can simulate quantum particles on a lattice. Such particle-lattice systems can be used as models for the behavior of high-temperature superconductors or the particles inside an atomic nucleus.

The superconducting cavity holds microwave radiation of specific frequencies, or modes, which are determined by the cavity’s size. The researchers change the effective size of the cavity by delaying the propagation of photons at one end by a variable interval. When the cavity contains multiple microwave photons, tuning its effective length causes the various cavity modes to interact with each other.

The team used this setup to create a so-called bosonic Creutz ladder—a simple model of particles moving on a lattice of four nodes. In their implementation of the model, Wilson and colleagues engineered the cavity-mode interactions so that each mode of the cavity corresponded to a node on the lattice. They also showed that the quantum simulator can be programmed in situ by introducing microwaves of different frequencies into the cavity. The technique can be scaled up to simulate more complex quantum systems by placing multiple superconducting cavities on the chip.

The team hopes to quickly scale up the size of their simulations and try to test new models.  They expect that the inherent programmability of the platform should make progress easier than for dedicated simulators design to simulate a single model.

Quantum Simulation of the Bosonic Creutz Ladder with a Parametric Cavity was published in Physical Review Letters on September 2, 2021.

Original synopsis by Sophia Chen for Physical Review Letters.

Copyright APS/Physics Magazine

This project is supported in part by the Canada First Research Excellence Fund through the Transforming Quantum Technologies (TQT) program.

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