Harvard’s ultra-thin chip could revolutionize quantum computing

Good news!

"Researchers at Harvard have created a groundbreaking metasurface that can replace bulky and complex optical components used in quantum computing with a single, ultra-thin, nanostructured layer. This innovation could make quantum networks far more scalable, stable, and compact. By harnessing the power of graph theory, the team simplified the design of these quantum metasurfaces, enabling them to generate entangled photons and perform sophisticated quantum operations — all on a chip thinner than a human hair. It's a radical leap forward for room-temperature quantum technology and photonics.

Key takeaways

• New research shows that metasurfaces could be used as strong linear quantum optical networks
• This approach could eliminate the need for waveguides and other conventional optical components
• Graph theory is helpful for designing the functionalities of quantum optical networks into a single metasurface

..."

"... created specially designed metasurfaces — flat devices etched with nanoscale light-manipulating patterns —  to act as ultra-thin upgrades for quantum-optical chips and setups. ..."

From the abstract of the perspective:

"A photon—the smallest discrete unit (quantum) of light—is a fundamental concept in various technologies such as secure communication and quantum computing. Identical photons can “feel” each other’s presence on a beam splitter, an optical device that separates a beam of light into distinct paths.

This so-called quantum interference is a straightforward method for generating quantum entanglement, in which two or more photons are linked regardless of their distance.

Entangling photons that travel across multiple paths is one of the primary challenges in quantum technologies. Existing devices occupy immense space for a handful of photonic qubits (quantum bits analogous to classical bits). ...

Yousef et al. (1) report a metasurface—a planar array of structures with sizes smaller than the wavelength of light—that can manage photons on demand. This produces a special class of quantum states in a miniature optical device with micrometer dimensions."

From the editor's summary and abstract:

"Editor’s summary

The bunching and antibunching of interfering single photons is a fundamental quantum effect that underpins the development of optical-based quantum computing and communication. Extending this Hong-Ou-Mandel (HOM) effect to larger systems requires an increasing number of bulky optical components that would be practically infeasible. Yousef et al. report on the use of metasurfaces as a multiport HOM interferometer and related quantum correlation measurements ... They also introduce a graph-theoretic formalism that represents both metasurface-based quantum optics and the resulting nonclassical correlation landscape. Such graphs can be used for the design of scalable, low-decoherence quantum information infrastructures. ...

Abstract

Multiphoton interference and entanglement are fundamental to quantum information science, yet extending these effects to higher-dimensional systems remains challenging given the imperfections and complexity of scaling conventional linear-optical setups.

We present a generalized Hong-Ou-Mandel effect using metasurfaces and graph theory, achieving controlled multiphoton bunching, antibunching, and entanglement across parallel Jones matrix–encoded spatial modes—all within a single-layer metasurface.

A graph-theoretic dual framework is introduced that simultaneously encodes the metasurface-based multiport interferometer designs and its resulting nonclassical correlations, enabling the direct translation of linear quantum optical networks into a single-layer metasurface.

We also demonstrate the ability of metasurfaces to produce multipath-entangled states and perform transformations equivalent to higher-order Hadamard interferometers. Our results underscore metasurface quantum graphs for scalable, low-decoherence quantum information infrastructure."

Harvard’s ultra-thin chip could revolutionize quantum computing | ScienceDaily "Researchers blend theoretical insight and precision experiments to entangle photons on an ultra-thin chip."

Researchers blend theoretical insight and precision experiments to entangle photons on an ultra-thin chip (original news release)

Flat optics produces quantum graphs (perspective, no public access) "A miniature device links multiple photon paths for bespoke entanglement"

Metasurface quantum graphs for generalized Hong-Ou-Mandel interference (no public access)

Schematic depiction of metasurface-based optical setup in the lab.