Hole spin qubits confined to lithographically - defined lateral quantum dots in Ge/SiGe heterostructures show great promise. On reason for this is the intrinsic spin - orbit coupling that allows all - electric control of the qubit. That same feature can be exploited as a coupling mechanism to coherently link spin qubits to a photon field in a superconducting resonator, which could, in principle, be used as a quantum bus to distribute quantum information. The work reported here advances the knowledge and technology required for such a demonstration. We discuss the device fabrication and characterization of different quantum dot designs and the demonstration of single hole occupation in multiple devices. Superconductor resonators fabricated using an outside vendor were found to have adequate performance and a path toward flip-chip integration with quantum devices is discussed. The results of an optical study exploring aspects of using implanted Ga as quantum memory in a Ge system are presented.
The ability to control the light-matter interaction with an external stimulus is a very active area of research since it creates exciting new opportunities for designing optoelectronic devices. Recently, plasmonic metasurfaces have proven to be suitable candidates for achieving a strong light-matter interaction with various types of optical transitions, including intersubband transitions (ISTs) in semiconductor quantum wells (QWs). For voltage modulation of the light-matter interaction, plasmonic metasurfaces coupled to ISTs offer unique advantages since the parameters determining the strength of the interaction can be independently engineered. In this work, we report a proof-of-concept demonstration of a new approach to voltage-tune the coupling between ISTs in QWs and a plasmonic metasurface. In contrast to previous approaches, the IST strength is here modified via control of the electron populations in QWs located in the near field of the metasurface. By turning on and off the ISTs in the semiconductor QWs, we observe a modulation of the optical response of the IST coupled metasurface due to modulation of the coupled light-matter states. Because of the electrostatic design, our device exhibits an extremely low leakage current of ∼6 pA at a maximum operating bias of +1 V and therefore very low power dissipation. Our approach provides a new direction for designing voltage-tunable metasurface-based optical modulators.
Here, we demonstrate coupled triple dot operation and charge sensing capability for the recently introduced quantum dot technology employing undoped Si/Si0.8Ge0.2 hetero-structures which also incorporate a single metal-gate layer to simplify fabrication. Si/SiGe hetero-structures with a Ge concentration of 20% rather than the more usual 30% typically encountered offer higher electron mobility. The devices consist of two in-plane parallel electron channels that host a double dot in one channel and a single dot in the other channel. In a device where the channels are sufficiently close a triple dot in a triangular configuration is induced leading to regions in the charge stability diagram where three charge-addition lines of different slope approach each other and anti-cross. In a device where the channels are further apart, the single dot charge-senses the double dot with relative change of ~2% in the sensor current.
Kalugin, Nikolai G.; Jing, Lei; Morell, Eric S.; Dyer, Gregory C.; Wickey, Lee; Ovezmyradov, Mekan; Grine, Albert D.; Wanke, Michael W.; Shaner, Eric A.; Lau, Chun N.; Foa Torres, Luis E.F.; Fistul, Mikhail V.; Efetov, Konstantin B.
Graphene has established itself as a promising optoelectronic material. Many details of the photoresponse (PR) mechanisms in graphene in the THz-to-visible range have been revealed, however, new intricacies continue to emerge. Interface junctions, formed at the boundaries between parts of graphene with different number of layers or different stacking orders, and making connection between electrical contacts, provide another peculiar setup to establish PR. Here, we experimentally demonstrate an enhanced polarization sensitive photoelectric PR in graphene sheets containing interface junctions as compared to homogenous graphene sheets in the visible, infrared, and THz spectral regions. Our numerical simulations show that highly localized electronic states are created at the interface junctions, and these states exhibit a unique energy spectrum and enhanced probabilities for optical transitions. The interaction of electrons from interface junction states with electromagnetic fields generates a polarization-sensitive PR that is maximal for the polarization direction perpendicular to the junction interface.
Shaner, Eric A.; Wanke, Michael W.; Grine, Albert D.; Kalugin, Nikolai G.; Jing, Lei J.; Morell, Eric S.; Dyer, Gregory C.; Wickey, Lee W.; Ovezmyradov, Mekan O.; Lau, Chun N.; F. Foa Torres, Luis E.; Fistul, Mikhail V.; Efetov, Konstantin B.