Spectroscopy and Application of Solid-State Quantum Centers

Summary

The past seventy years of semiconductor research has led to a paradigm shift: defects as the device. The Quantum Center program aims to leverage the quantum properties of color center point defects in semiconductors to enable applications in photonics, better understand conventional semiconductor device performance, and develop applications like quantum sensing and quantum communication. Such solid-state systems exhibit many of the same features of atomic, molecular, and optical (AMO) systems but in a stable, solid-state platform. 

Description

Individual quantum center creation, characterization, quantum control, efficient collection and readout.

Credit: NIST

Quantum color centers in wide-bandgap semiconductors have spin and optical degrees of freedom, which can be leveraged for applications such as sensing and single-photon generation. In materials like diamond and silicon carbide, long spin lifetimes and quantum coherence times enable sensitive detection of magnetic fields, temperature, and pressure, among other measurands. Strong spin-dependent optical transitions at low temperatures provide a platform for distributing spin entanglement via coherent photons. Over the last two decades, interest in color centers has led to breakthrough quantum demonstrations such as few-node quantum networks and the commercialization of diamond nitrogen-vacancy (NV center) quantum microscopes using single-defect tips as nanoscale magnetic field sensors with unprecedented spatial resolution. Despite these successes, technology based on color centers is limited by pervasive issues in the field, namely nonuniform properties and low-fidelity readout.

The program aims to develop color center platforms as a test vehicle to overcome the technical challenges inherent in these host materials, enable applications in photonics, better understand conventional semiconductor device performance, and develop applications like quantum sensing and quantum communication. We are developing spectroscopic characterization protocols and materials processing/fabrication protocols to control the environment surrounding the defects and characterize color center properties both for ensembles and individual centers at ambient and cryogenic temperatures. To improve quantum sensing efficiency and sensitivity, we develop adaptive algorithms that use real-time data to optimize acquisition, enhancing ongoing characterization efforts. We are developing photonic structures to facilitate efficient photon out-coupling, such as gratings and cavities. We are incorporating integrated photonic detection schemes (e.g., superconducting nanowire single photon detectors on waveguides), eliminating issues with measuring weak optical signals. Additionally, we are active in deterministic color center fabrication and novel pathways toward smaller device footprints and increased sensitivity. 

Quantum diamond microscope

Credit: NIST

Unlike diamond, quantum centers in silicon represent a relatively nascent topic in the field. Still, they are generating substantial interest for their ease of fabrication and doping, the promise of device density/scalability, efficient emission at telecom wavelengths, and ease of integration with electronics and photonics. Silicon-based quantum centers lack an understanding of the structure and preparation of the color centers, and many observed emitters have debated conformations and lack optimized fabrication protocols. To produce the first demonstration of electrically pumped single-photon sources in silicon, we are working first to identify and develop robust fabrication of quantum centers in silicon. Next, we work to incorporate quantum centers with conventional electronic and photonic devices without destroying them, or vice-versa, to extract the greatest functionality. Further, while the cryogenic operation conditions lead to excellent properties and compatibility with quantum applications, we are working to ensure fidelity with non-cryogenic instruments. We will develop metrology and fabrication techniques to identify and prepare solid-state quantum centers themselves, as well as integrated architectures for sensing and quantum information applications that cannot be addressed by superconducting or trapped atom/ion devices.