Quantum Photonics’ Breakthrough Promises a New Era for Powerful Optical Circuits

This world-first method for enabling quantum optical circuits using photons-light particles – opens up a new future in secure communication and quantum computing.

Modern technology is powered by the electrical circuitry of a chip, which is the semiconductor chip that underpins computers, cell phones, and other applications. Humans will create 175 zettabytes (175 trillion megabytes) of new information by 2025. How do we protect sensitive data in such high volumes? Given our limited computing power, how can we tackle grand-challenge-like issues, such as privacy, security, and climate change, and leverage this data?

Emerging quantum communication and computation technology is a promising alternative. This will, however, require the widespread development and deployment of quantum optical circuits capable of processing the vast amounts of information generated daily. The University of Southern California was founded in 1880 and is one of the world’s most prestigious private research universities. It is located in the heart of Los Angeles.” data-gt-translate-attributes=’ [“attribute”: “data-cm tooltip,” “format”: “html”]’> USC’s Mork Family Department of Chemical Engineering and Materials Science has made a breakthrough to help enable this technology.

A traditional electrical circuit is a path along which electrons of an electric charge flow. However, a quantum optical system uses light sources to generate individual light particles or photons on demand. These light particles act as information-carrying bits (quantum bits, qubits). These “quantum dots,” tiny semiconductors, are small-sized collections of tens to a million atoms. They are buried in a matrix made of another suitable semiconductor.

They are the most versatile single-photon generators available on demand. These single photon sources must consistently be placed on a semiconductor chip to make an optical circuit. The photons must be released from sources with almost identical wavelengths in a controlled direction. This allows them to interact with other particles and photons to transmit and process information.

This has been a significant barrier to developing such circuits. Quantum dots, currently manufactured in different sizes and shapes, are assembled on the chip randomly. Because the beads are other in size and shape, the emitted photons do not have uniform wavelengths. Because of this and their lack of positional order, they need to be more suitable for developing optical circuits.

Researchers at USC recently published work showing single photons can be produced from quantum dots arranged in a specific pattern. The method of aligning quantum dots was developed by Professor Anupam Madhukar and his team at USC almost thirty years ago. This is well before the current explosion in quantum information research and interest in single-photon sources on-chip. The USC team used these methods to create single-quantum dot structures with remarkable single-photon emission properties. The ability to align uniformly emitting quantum dots precisely will allow for producing optical circuits. This could lead to new advancements in quantum computing.

Jiefei Zhu, currently a research assistant professor at the Mork Family Department for Chemical Engineering and Materials Science with Anupam Madhukar (Kennett T. Norris Professor of Engineering and Professor of Chemical Engineering and Electrical Engineering, Materials Science and Physics), led the work.

Zhang stated that the breakthrough opens the door to the following steps: lab demonstrations of single-photon physics and chip-scale fabrications of quantum photonic circuits. This has potential quantum applications (secure) communication and imaging, sensing, and quantum simulations, computation.

Madhukar stated that it was essential for quantum dots to be ordered in a specific way so that photons from any two or three drops could be controlled to connect on the chip. This will be the foundation of quantum optical circuit building units.

Madhukar stated, “If the source from which the photons originate is randomized, this cannot occur.”

The silicon-integrated electronic chip is the basis of current technology, which allows us to communicate online. Madhukar stated that if the transistors on this chip were not placed in precisely designed locations, there wouldn’t be an integrated electrical circuit. It is the requirement that photon sources, such as quantum dots, be placed in precise locations to create quantum optical systems.

“This is an important example of how solving fundamental material science challenges, such as how to create quantum dots in precise position and composition, can have huge downstream implications for technologies, like quantum computing,” said Evan Runnerstrom (program manager, Army Research Office), an element of U.S Army Combat Capabilities Development Command’s Army Research Laboratory. This is a clear example of how ARO’s targeted investments into basic research support the Army’s enduring modernization efforts, such as networking.

The team used a technique called SESRE (substrate-encoded size-reducing epitaxy), which the Madhukar group developed in the early 1990s to create the exact layout of quantum dots in circuits. The current work involved the fabrication of regular arrays containing mesas measuring in the nanometers (Fig. 1(a), which has a defined edge orientation (sidewalls), shape, and depth on a flat semiconductor substrate made of gallium arsenide (GaAs). The following method is used to create quantum dots on top of these mesas:

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