We demonstrate quantum Hall resistance measurements with metrological accuracy in a small cryogen-free system operating at a temperature of around 3.8 K and magnetic fields below 5 T. Operating this system requires little experimental knowledge or laboratory infrastructure, thereby greatly advancing the proliferation of primary quantum standards for precision electrical metrology. This significant advance in technology has come about as a result of the unique properties of epitaxial graphene on SiC.
A technique for the fabrication of small (2–10 μm in diameter) microlenses on the surface of glass with embedded silver nanoclusters in a subsurface diffusion layer is demonstrated. The dependence of the microlens size on the exposure time and the laser power of a focused continuous wave (cw) laser beam is discussed. It is shown that the optical transmission of the lenses increases with increasing laser power used for the exposure. The temperature distribution in the glass around the focal spot is calculated taking into account the temperature dependence of heat conductivity, shape of the beam, and decrease of absorption coefficient with depth through the diffusion layer containing Ag clusters. The measured microlens sizes are in good agreement with the calculations.
We report coherent frequency conversion in the gigahertz range via three-wave mixing on a single artificial atom in open space. All frequencies involved are in vicinity of transition frequencies of the three-level atom. A cyclic configuration of levels is therefore essential, which we have realised with an artificial atom based on the flux qubit geometry. The atom is continuously driven at two transition frequencies and we directly measure the coherent emission at the sum or difference frequency. Our approach enables coherent conversion of the incoming fields into the coherent emission at a designed frequency in prospective devices of quantum electronics.For a long time research in experimental quantum optics focused on studying ensembles of natural atoms [1,2]. However, there have been huge advances in performing analogous quantum optics experiments using other systems [3][4][5]. In particular, superconducting artificial atoms are remarkably attractive to study quantum optics phenomena. The artificial atoms are nano-scale electronic circuits that can be fabricated using well established techniques and can therefore be easily scaled up to larger systems. Their energy levels can be engineered as desired, and strong coupling can be achieved with resonators and transmission lines [6][7][8][9]. This greater control of parameters allows one to reproduce quantum optics phenomena with improved clarity or even reach regimes, that are unattainable with natural atoms. For instance coherent population trapping [10], electromagnetically induced transparency [11,12], Autlers-Townes splitting [13][14][15][16][17], and quantum wave mixing [18] have been experimentally observed in superconducting threelevel systems [19][20][21][22][23]. Moreover, three-level atoms can be used to cool quantum systems [24,25], amplify microwave signals [26] and generate single or entangled pairs of photons [27] -important applications for future quantum networks. Here we investigate three-wave mixing, a nonlinear optical effect that can occur in cyclic threelevel atoms, which are lacking in nature [28], but can easily be realised with superconducting artificial atoms. The only suitable natural systems for the three-wave mixing are chiral molecular three-level systems without inversion symmetry [29]. However, these systems cannot be tuned in frequency. Different to Josephson junction based parametric three-wave mixing devices [30], that rely on mixing on a classical non-linearity, we implement here another method to generate three-wave mixing using a single cyclic or ∆-type artificial atom. This was considered theoretically in references [28,31].We directly measure the coherent emission of the cyclic three-level atom under two external drives corresponding to two atomic transitions. The emission occurs at a sin-gle mixed frequency (sum or difference). This emission is a corollary of coherent frequency conversion but inherently differs from classical frequency conversion [32,33] which would result in sidebands at the sum and difference frequencies. ...
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