Quantum Computers Untangle Knotty Polymer Problem

(PhysicsWorld) In a collaboration between the Scuola Internazionale Superiore di Studi Avanzati in Trieste and Trento University in Trento, Cristian Micheletti, Philipp Hauke and Pietro Faccioli used a specialist quantum computer called a quantum annealer to predict configurations of polymer chains. In doing so, Micheletti says they first had to “recast the basic models of polymer physics so that they can be used in a quantum computing framework”, anticipating that quantum technology will be the driving force behind scientific computing in the future.
Studying polymers is a computational challenge. The simplest model of polymers treats them as continuous paths on a regular lattice. But the numbers of possible paths (that is, the number of ways a polymer chain can fold and contort) are too numerous to calculate, even for a powerful supercomputer. On top of that, not all possible paths are chemically valid – some polymers do not allow chains that branch into two, while others will not allow loops. This task of sampling valid conformations from a dauntingly large search space is a central problem in polymer physics.
In their study published in Physical Review Letters, the researchers devised a way to map the problem of identifying valid polymer conformations onto a problem that is somewhat more tractable: minimizing the energy of a quantum system. To do this, they encoded the rules for polymer conformations onto a mathematical object called a Hamiltonian that describes the energy dynamics of a quantum system. The lowest-energy quantum state of this Hamiltonian contains only those arrangements of polymer chains that obey the rules.