Synopsis

Making Hard Problems for Quantum Computers

Physics 9, s77
Researchers have developed a computer algorithm that doesn’t solve problems but instead creates them for the purpose of evaluating quantum computers.
Courtesy of D-Wave Systems Inc.

The desire for quantum computers stems from their potential to solve certain hard problems faster than classical computers. But those bragging rights haven’t actually been earned yet, as no experiment has shown this presumed speedup. Researchers from the University of Southern California, Los Angeles, and the Complutense University of Madrid, Spain, have devised an algorithm that generates extra hard problems that could offer quantum computers the chance to prove their worth.

The problems that the team focused on belong to the general class of optimization problems. The main example is the Ising model, which describes the interaction of a large number of spins within a lattice. The goal is to find the ground state, which is the orientation of spins that minimizes the interaction energy. The problem is computationally hard because there are many local minima (pseudo-ground-states) that can fool a search algorithm.

Quantum computers—specifically so-called quantum annealers—offer promise for efficiently solving the Ising model and other optimization problems by using quantum superposition to sample all possible minima simultaneously. To test this potential, researchers have randomly generated Ising-type problems tailored to the size of current quantum annealers, such as the 512-qubit D-Wave Two processor. Unfortunately, for this relatively small size, quantum annealers do not show a significant improvement over classical counterparts. In the new study, the researchers propose a way of identifying harder problems so that differences become starker. They have devised an algorithm that starts with a random Ising-type problem and then optimizes the hardness, which is defined by the solution time for a classical computer. The team showed that they could increase the hardness by more than 2 orders of magnitude.

This research is published in Physical Review A.

–Michael Schirber

Michael Schirber is a Corresponding Editor for Physics based in Lyon, France.


Subject Areas

Quantum Information

Related Articles

How to Speed up a Quantum Network
Quantum Information

How to Speed up a Quantum Network

Sending photons to a remote site in groups should allow quantum links to be more rapidly established across future quantum networks than if photons are sent one at a time. Read More »

Erasure Qubits for Abridged Error Correction
Quantum Information

Erasure Qubits for Abridged Error Correction

Researchers have realized a recently proposed qubit in which the errors mostly involve erasure of the qubit state, an advance that could help simplify the architecture of fault-tolerant quantum computers. Read More »

Fault-Tolerant Quantum Error Correction without Measurements
Quantum Physics

Fault-Tolerant Quantum Error Correction without Measurements

A proposed recipe for quantum error correction removes the need for time-consuming measurements of qubits, replacing them with copying and feedback steps instead. Read More »

More Articles