Thrust 3 will focus on engineering material platforms that host localized quantum states with robust coherence. These states will be interfaced with quantum photonic and phononic degrees of freedom to realize quantum networks. A key part of this thrust will be the detailed investigation and control of ubiquitous interface-induced decoherence that limits quantum technologies. The model systems explored here will serve to inform a decoherence mitigation approach in a much broader set of materials that host quantum states, including those in Thrusts 1 & 2 as well as those explored by the Foundry’s industrial and network partners.
Activities in Thrust 3 will include defect and interface engineering of Foundry materials such as spin qubits in diamond and III-V hosts, first-principles modeling of defect states in novel material systems with potential as qubits, experimental characterization of decoherence at interfaces, theoretical investigation of decoherence origins, and high-fidelity integration of ultra-low loss optical and acoustic elements with spin qubits. Model spin systems will be used as testbeds for decoherence studies and for adiabatic quantum computing. The overall goal is to accelerate the integration of promising qubit platforms into next-generation quantum technologies.
- QF Thrust 3 – Year 1 Summary
In the first year, the Moody and Bowers groups made significant progress demonstrating ultra-bright, high purity entangled photon pair sources from aluminum gallium arsenide on insulator (AlGaAsOI) microring resonators. The initial demonstration on this new quantum photonic integrated circuit (QPIC) platform represents a nearly 1,000-fold improvement in brightness compared to existing sources. The waveguide-integrated source exhibits an internal entangled photon pair generation rate greater than 20×109 pairs s-1 mW-2, emits near 1550 nm, produces heralded single photons with >99% purity, and violates Bell’s inequality by more than 40 standard deviations with visibility >97%. Combined with the high optical nonlinearity and optical gain of AlGaAs for active component integration, these are all essential features for a scalable quantum photonic platform. Their work has recently been accepted for publication in PRX Quantum in 2021 . Their review on chip-scale nonlinear quantum photonics was also published in the first year which is a great summary of the current state-of-the-art for nonlinear quantum photonic light sources . In year 2, the group hopes to explore other critical components required for a fully on-chip QPIC including on-chip filters, single and two- qubit gates, and tunable laser sources.
The Weld group pushed forward two different experiments on quantum transport phenomena. The first experiment demonstrated the ability to transport a Bose-Einstein condensate (BEC) across an inhomogeneous force landscape via periodically driving near the Bloch frequency, and unearthed a deep connection between drive phase and Poincaré orbit structure. This work has been published in Physical Review Research . The second experiment investigates signatures of many-body dynamical (de-)localization in the quantum kicked rotor. By repeatedly “kicking” an interacting BEC with an optical lattice, the group is experimentally probing the ways in which many-body quantum systems absorb energy or fail to do so. This project has nucleated two extramural collaborations, with Subhadeep Gupta’s group at the University of Washington and with Victor Galitski’s group at the JQI. A separate theoretical collaboration on Foundry-relevant topics with the Vishveshwara group at UIUC has resulted in a recent arXiv manuscript on the bosonic Kitaev chain . A future prospect of current interest is to apply recently-developed periodic driving techniques to create a new class of matter-wave interferometer for applications in quantum force sensing.
The Bleszynski Jayich group has worked to commission a state-of-the-art diamond growth facility. This facility will allow the efficient production of homoepitaxial diamond and create high-quality films with embedded solid-state qubits. A novel electron irradiation system, eventually integrated with a substrate heater, will allow our group to access a promising new simultaneous irradiation and annealing method for nitrogen-vacancy (NV) creation. The first part of the electron irradiation system is currently under active use in preparing thin films of NVs. In addition to this, our group has been researching avenues to perfect our diamond growth techniques further. We have published work outlining the effect of substrate miscut on the growth quality of our films and the quantum properties of different types of grown NVs . In the second year, we will explore novel growth techniques using a newly minted growth chamber designed with experimental growth in mind.
 T. J. Steiner et al., “Ultra-bright entangled-photon pair generation from an AlGaAs-on-insulator microring resonator,” arXiv:2009.13462, Sep. 2020.
 G. Moody, L. Chang, T. J. Steiner, and J. E. Bowers, “Chip-Scale Nonlinear Photonics for Quantum Light Generation,” Accept. AVS Quantum Sci., 2020.
 A. Cao, R. Sajjad, E.Q. Simmons, C.J. Fujiwara, T. Shimasaki, and D.M. Weld, Phys. Rev. Research 2, 032032 (2020)
 S. Vishveshwara and D.M. Weld, arXiv:2012.02380 (2020)
 S. A. Meynell, C. A. McLellan, L. B. Hughes, W. Wang, T. Mates, K. Mukherjee, and A. C. Bleszynski Jayich. Engineering quantum-coherent defects: The role of substrate miscut in chemical vapor deposition diamond growth. Applied Physics Letters, 117 19, 194001 (2020)