A Zhao Blurb Figure

Reducing the measurement complexity of variational quantum algorithms

A Zhao Blurb Figure

Andrew Zhao and Akimasa Miyake, with collaborators from Tufts University and Caltech, have published a paper in Physical Review A in which they propose a technique to reduce the number of circuit repetitions required to implement variational quantum algorithms. Such algorithms are designed for the hardware limitations of present-day quantum computers. Instead of performing one long, sophisticated quantum circuit, variational algorithms repeatedly run and measure the outputs of shorter, more feasible circuits, and then use classical optimization techniques to arrive at a solution. Typically, one uses these algorithms to calculate physical quantities, such as the energy of a chemical system.

However, the number of variational circuit repetitions required can be overwhelming, especially when simulating chemistry. To address this issue, the paper introduces a method to group together compatible measurements which may be performed simultaneously, in exchange for slightly longer circuits. To demonstrate the practical effectiveness of this technique, the authors present numerical calculations in the context of simulating various chemical molecules. They observe a roughly tenfold reduction in the number of required measurements, and they furthermore confirm this effectiveness in general with analytical proofs.

The full article can be found online at https://link.aps.org/doi/10.1103/PhysRevA.101.062322.

A many-body quantum system

Subsystem symmetry enabling quantum computation

Austin Daniel, Rafael Alexander, and Akimasa Miyake have published a paper in the journal Quantum demonstrating that certain many-body quantum systems, when placed on lattices with different geometries, can possess a variety of exotic “subsystem symmetries” that can be utilized to empower quantum computation.

It has long been an open problem to understand which quantum many-body states are useful for measurement-based quantum computing (MBQC), a scheme whereby local measurements on a large, entangled quantum state drive a computational process.

In the past, it was suggested that such systems should possess special topological properties with respect to a symmetry, known as symmetry protected topological order (SPTO).

Traditionally, these many-body systems were studied in terms of a global symmetry that acts uniformly on every site in the lattice; however, recent work has highlighted the importance of subsystem symmetries, which act on special subsets of the lattice.

The authors show that for a variety of lattices there are large families of many-body systems that posses a common subsystem SPTO, ensuring that any such system is a resource for MBQC.

This demonstrates that resources for MBQC extend far beyond what was previously known.

The full article can be found online at https://quantum-journal.org/papers/q-2020-02-10-228/.

An example of a subsystem symmetry that protects the cluster-phase on the (3,4,6,4) Archimedean lattice.

UNM to participate in $15 million NSF program to create first practical quantum computer














A research team of the University of New Mexico led by CQuIC faculty, Akimasa Miyake, will participate in a $15 million, multi-university collaboration as part of a National Science Foundation program designed with the audacious goal of building the world’s first practical quantum computer. Read the UNM news article.

Team of STAQ-project researchers at Ideas Lab meeting at the Santa Fe Institute in Fall 2017. Front row (l. to r.): Hartmut Haeffner (University of California, Berkeley), Aram Harrow (Massachusetts Institute of Technology), and Kenneth Brown (Duke University). Back row l. to r.): Akimasa Miyake (University of New Mexico), Alexey Gorshkov (University of Maryland College Park), Jungsang Kim (Duke University), Peter Love (Tufts University), Christopher Monroe (University of Maryland College Park), and Frederic Chong (University of Chicago).

Symmetric Phases of Universal Quantum Computation

Jacob Miller and Akimasa Miyake have recently published a paper in Physical Review Letters giving strong evidence that certain forms of symmetric topological quantum matter can be utilized ubiquitously to power quantum computation. Their work is carried out within measurement-based quantum computation, where computation is extracted from a fixed quantum “resource state” using local measurements. In this setting, the power of computation attributes the physical properties of the resource state, but the properties which guarantee a state can carry out universal quantum computation are still unknown.
In their work, the authors study a model of symmetric topological matter and identify special states in each phase which enable universal quantum computation precisely when they possess nontrivial quantum order. This gives an infinite family of new universal resource states whose structure perfectly mirrors a recent classification of symmetric quantum order coming from condensed matter physics. These special resource states are distinguished by their “fractional symmetry”, a property already noticed in previous universal resource states, but which hadn’t been investigated systematically. Overall, the work provides a concrete research program for identifying phases of universal quantum computation within the setting of symmetric quantum matter.
The full article can be found online at Phys. Rev. Lett. 120, 170503 (2018).
Classification of special resource states with fractional symmetry.