Near-Field Scanning Microwave Microscopy in the Single Photon Regime

The microwave properties of nano-scale structures are important in a wide variety of applications in quantum technology. Here we describe a low-power cryogenic near-field scanning microwave microscope (NSMM) which maintains nano-scale dielectric contrast down to the single microwave photon regime, up to $10^{9}$ times lower power than in typical NSMMs. We discuss the remaining challenges towards developing nano-scale NSMM for quantum coherent interaction with two-level systems as an enabling tool for the development of quantum technologies in the microwave regime

Effects of quasiparticle tunneling in a circuit-QED realization of a strongly driven two-level system

We experimentally and theoretically study the frequency shift of a driven cavity coupled to a superconducting charge qubit. In addition to previous studies, we here also consider drive strengths large enough to energetically allow for quasiparticle creation. Quasiparticle tunneling leads to the inclusion of more than two charge states in the dynamics. To explain the observed effects, we develop a master equation for the microwave dressed charge states, including quasiparticle tunneling. A bimodal behavior of the frequency shift as a function of gate voltage can be used for sensitive charge detection. However, at weak drives the charge sensitivity is significantly reduced by non-equilibrium quasiparticles, which induce transitions to a non-sensitive state. Unexpectedly, at high enough drives, quasiparticle tunneling enables a very fast relaxation channel to the sensitive state. In this regime, the charge sensitivity is thus robust against externally injected quasiparticles and the desired dynamics prevail over a broad range of temperatures. We find very good agreement between theory and experiment over a wide range of drive strengths and temperatures.Comment: 25 pages, 7 figure

Circular photon drag effect in bulk tellurium

The circular photon drag effect is observed in a bulk semiconductor. The photocurrent caused by a transfer of both translational and angular momenta of light to charge carriers is detected in tellurium in the mid-infrared frequency range. Dependencies of the photocurrent on the light polarization and on the incidence angle agree with the symmetry analysis of the circular photon drag effect. Microscopic models of the effect are developed for both intra- and inter-subband optical absorption in the valence band of tellurium. The shift contribution to the circular photon drag current is calculated. An observed decrease of the circular photon drag current with increase of the photon energy is explained by the theory for inter-subband optical transitions. Theoretical estimates of the circular photon drag current agree with the experimental data.Comment: 8 pages, 4 figure

Dynamic parity recovery in a strongly driven Cooper-pair box

We study a superconducting charge qubit coupled to an intensive electromagnetic field and probe changes in the resonance frequency of the formed dressed states. At large driving strengths, exceeding the qubit energy-level splitting, this reveals the well known Landau-Zener-Stuckelberg (LZS) interference structure of a longitudinally driven two-level system. For even stronger drives we observe a significant change in the LZS pattern and contrast. We attribute this to photon-assisted quasiparticle tunneling in the qubit. This results in the recovery of the qubit parity, eliminating effects of quasiparticle poisoning and leads to an enhanced interferometric response. The interference pattern becomes robust to quasiparticle poisoning and has a good potential for accurate charge sensing.Comment: 5 pages, 4 figure

Can an electric current orient spins in quantum wells?

A longstanding theoretical prediction is the orientation of spins by an electrical current flowing through low-dimensional carrier systems of sufficiently low crystallographic symmetry. Here we show by means of terahertz transmission experiments through two-dimensional hole systems a growing spin orientation with an increasing current at room temperature.Comment: 5 pages, 2 figure

The familiar area hypothesis and movement patterns of wild forest reindeer in Karelia, Northern Europe

The relevance of the familiar area hypothesis to the behaviour of the wild forest reindeer (Rangifer tarandus fennicus Lönnb.) was studied in a Fenno-Soviet project by radio and field tracking of these ungulates in Karelia, Northern Europe, in 1978 - 1985. This subpopulation (500 - 600 exx.) has a tradition of overwintering in a restricted area around Lake Lentua (ca. 1000 km2). The spring migration period is shorter in length than the autumn migration. The migration routes are generally the same in autumn and spring, although exceptions occur, indicating exploratory behaviour. The large winter herds disband into small groups or lone individuals for the summertime, when this subpopulation is spread over a much wider area (ca. 5400 km2). It is concluded that the observations made support the familiar area hypothesis in all essential points

Global in Time Solutions to Kolmogorov-Feller Pseudodifferential Equations with Small Parameter

The goal in this paper is to demonstrate a new method for constructing global-in-time approximate (asymptotic) solutions of (pseudodifferential) parabolic equations with a small parameter. We show that, in the leading term, such a solution can be constructed by using characteristics, more precisely, by using solutions of the corresponding Hamiltonian system and without using any integral representation. For completeness, we also briefly describe the well-known scheme developed by V.P.Maslov for constructing global-in-time solutions.Comment: 27 page

Fast tunable high Q-factor superconducting microwave resonators

We present fast tunable superconducting microwave resonators fabricated from planar NbN on a sapphire substrate. The $3\lambda/4$ wavelength resonators are tuning fork shaped and tuned by passing a dc current which controls the kinetic inductance of the tuning fork prongs. The $\lambda/4$ section from the open end operates as an integrated impedance converter which creates a nearly perfect short for microwave currents at the dc terminal coupling points, thus preventing microwave energy leakage through the dc lines. We measure an internal quality factor $Q_{\rm int}>10{^{5}}$ over the entire tuning range. We demonstrate a tuning range of $> 3\%$ and tuning response times as short as 20 ns for the maximum achievable detuning. Due to the quasi-fractal design, the resonators are resilient to magnetic fields of up to 0.5 T