EFRI ACQUIRE: Integrated Nanophotonic Solid State Memories for Telecom Wavelength Quantum Repeaters

Yale University, New Haven CT

Investigators

Abstract

Abstract Title: Development of quantum memory and photonic chip technologies for relaying long distance secure communications and connecting remote quantum networks Abstract: Non-technical description: Secure data communications are essential for commerce and national security. Current encryption methods rely on computational hardness, assuming that an adversary has limited computational power to break the encryption. Quantum computing using computers operating on quantum information instead of classical information challenges this paradigm, since the computational power of quantum computers is different from that of existing computers, with the exact boundaries still unknown. At the same time, communication using quantum technologies can provide security guaranteed by the fundamental laws of physics instead of computational hardness. This is based on the "no-cloning theorem" of quantum mechanics, which states that quantum information cannot be copied and is therefore resistant to eavesdropping in any form. Current implementations of quantum communication systems are limited to distances less than several hundred kilometers because the transmission of light through optical fibers is attenuated significantly at these lengths. This is vastly insufficient to reach across a continent or an ocean. Classical communications systems overcome this obstacle by using repeaters, which are amplifiers that boost the signal strength periodically over a long link. This technology cannot be applied to quantum information, because amplification is forbidden by the no-cloning theorem. Protocols have been developed to extend the range of quantum communications indefinitely using quantum memories that can store quantum information. These are referred to as "quantum repeaters", although they do not amplify signals and are only loosely analogous to repeaters for classical communications networks. The basic elements of a quantum repeater system have been demonstrated in proof-of-principle laboratory experiments; however, this technology cannot practically be scaled to large systems. The proposing team will develop scalable technologies for quantum repeaters, including new quantum memories, efficient interfaces to integrate and use those memories, and new protocols for quantum communication. The project focuses on designing optical nano-structures to efficiently interface with single-atom impurities in solids that act as quantum memories, as well as to efficiently detect and frequency-convert single photons. Additionally, the team will explore the theory of quantum information systems to identify ways to leverage the specific capabilities of these experimental systems, which will result in new protocols and encodings for quantum networks. Technical description: The overall goal of this project is to develop chip-scale, integrated, nanophotonic components for scalable, long-distance quantum communication based on a quantum repeater architecture. The team will address all three thrusts of the ACQUIRE program with the following specific goals: 1) Material characterization and engineering at the quantum level to develop new atom-like systems in the solid state (color centers in diamond, rare earth ions) to use as quantum memories and single photon sources, and device engineering to integrate these systems with nanophotonic cavities and waveguides to enhance atom-photon interaction; 2) Heterogeneous integration of low loss, wideband ÷(2) waveguides on silicon substrates for realizing wavelength converters as a key enabling technology for efficient quantum memories and room temperature detectors, scalable photon pair sources, and low loss electro-optic modulators; 3) Low loss fiber-to-chip interfaces using adiabatic fiber tapering and waveguide 3D tapering; 4) Theoretical development and analysis of quantum repeater protocols based on specific experimental platforms being studied, in order to guide engineering efforts and identify trade-offs; 5) Simultaneous demonstration of key elements of quantum repeater protocols (including spin-photon entanglement, entanglement with ancilla nuclear spins for long-lived quantum memories, and remote entanglement swapping) using a fiber test-bed platform.