11 research outputs found
Symmetric Autocompensating Quantum Key Distribution
We present quantum key distribution schemes which are autocompensating
(require no alignment) and symmetric (Alice and Bob receive photons from a
central source) for both polarization and time-bin qubits. The primary benefit
of the symmetric configuration is that both Alice and Bob may have passive
setups (neither Alice nor Bob is required to make active changes for each run
of the protocol). We show that both the polarization and the time-bin schemes
may be implemented with existing technology. The new schemes are related to
previously described schemes by the concept of advanced waves.Comment: 4 pages, 2 figur
Verification of Wiedemann-Franz law in silver with moderate residual resistivity ratio
Electrical and thermal transport were studied in a vacuum-annealed
polycrystalline silver wire with residual resistivity ratio 200-400, in the
temperature range 0.1-1.2K and in magnetic fields up to 5T. Both at zero field
and at 5T the wire exhibits the Wiedemann-Franz law with the fundamental Lorenz
number, contrary to an earlier report [Gloos, K. et al, Cryogenics 30, 14
(1990)]. Our result demonstrates that silver is an excellent material for
thermal links in ultra-low-temperature experiments operating at high magnetic
fields.Comment: 8 pages, 3 figure
High performance cryogen-free microkelvin platform
Improved accessibility to the microkelvin temperature regime is important for
future research in quantum materials; for quantum information science; and for
applications of quantum sensors. Here we report the design and performance of a
microkelvin platform based on a nuclear demagnetization stage, engineered and
well optimized for operation on a standard cryogen-free dilution refrigerator.
PrNi5 is used as the dominant refrigerant. The platform provides a large area
for mounting experiments in an ultralow temperature, low electromagnetic noise
environment. The performance is characterized using current sensing noise
thermometry. Temperatures as low as 395 K have been reached, and a
protocol has been established in which it is possible to operate experiments
below 1 mK for 95% of the time, providing an efficient cryogen-free microkelvin
environment for a wide range of science applicationsComment: 8 pages, 5 figure
Microstructuring YbRh2Si2 for resistance and noise measurements down to ultra-low temperatures
We acknowledge funding by the German Research Foundation (DFG) via the TRR 288 (422213477, project A03, A10 and B02) and projects KR3831/4-1 and BR 4110/1-1. This work was supported by the EU H2020 European Microkelvin Platform EMP, Grant No. 824109.The discovery of superconductivity in the quantum critical Kondo-lattice system YbRh2Si2 at an extremely low temperature of 2 mK has inspired efforts to perform high-resolution electrical resistivity measurements down to this temperature range in highly conductive materials. Here we show that control over the sample geometry by microstructuring using focused-ion-beam techniques allows to reach ultra-low temperatures and increase signal-to-noise ratios (SNRs) tenfold, without adverse effects to sample quality. In five experiments we show four-terminal sensing resistance and magnetoresistance measurements which exhibit sharp phase transitions at the Néel temperature, and Shubnikov–de-Haas (SdH) oscillations between 13 T and 18 T where we identified a new SdH frequency of 0.39 kT. The increased SNR allowed resistance fluctuation (noise) spectroscopy that would not be possible for bulk crystals, and confirmed intrinsic 1/f -type fluctuations. Under controlled strain, two thin microstructured samples exhibited a large increase of TN from 67 mK up to 188 mK while still showing clear signatures of the phase transition and SdH oscillations. Superconducting quantum interference device-based thermal noise spectroscopy measurements in a nuclear demagnetization refrigerator down to 0.95 mK, show a sharp superconducting transition at Tc=1.2 mK. These experiments demonstrate microstructuring as a powerful tool to investigate the resistance and the noise spectrum of highly conductive correlated metals over wide temperature ranges.Publisher PDFPeer reviewe
A-B Transition in Superfluid <sup>3</sup>He and Cosmological Phase Transitions
First-order phase transitions in the very early universe are a prediction of many extensions of the Standard Model of particle physics and could provide the departure from equilibrium needed for a dynamical explanation of the baryon asymmetry of the Universe. They could also produce gravitational waves of a frequency observable by future space-based detectors such as the Laser Interferometer Space Antenna. All calculations of the gravitational wave power spectrum rely on a relativistic version of the classical nucleation theory of Cahn-Hilliard and Langer, due to Coleman and Linde. The high purity and precise control of pressure and temperature achievable in the laboratory made the first-order A to B transition of superfluid 3He ideal for test of classical nucleation theory. As Leggett and others have noted, the theory fails dramatically. The lifetime of the metastable A phase is measurable, typically of order minutes to hours, far faster than classical nucleation theory predicts. If the nucleation of B phase from the supercooled A phase is due to a new, rapid intrinsic mechanism that would have implications for first-order cosmological phase transitions as well as predictions for gravitational wave production in the early universe. Here we discuss studies of the A-B phase transition dynamics in 3He, both experimental and theoretical, and show how the computational technology for cosmological phase transition can be used to simulate the dynamics of the A-B transition, support the experimental investigations of the A-B transition in the QUEST-DMC collaboration with the goal of identifying and quantifying the mechanism(s) responsible for nucleation of stable phases in ultra-pure metastable quantum phases
Cooling low-dimensional electron systems into the microkelvin regime.
Two-dimensional electron gases (2DEGs) with high mobility, engineered in semiconductor heterostructures host a variety of ordered phases arising from strong correlations, which emerge at sufficiently low temperatures. The 2DEG can be further controlled by surface gates to create quasi-one dimensional systems, with potential spintronic applications. Here we address the long-standing challenge of cooling such electrons to below 1 mK, potentially important for identification of topological phases and spin correlated states. The 2DEG device was immersed in liquid 3He, cooled by the nuclear adiabatic demagnetization of copper. The temperature of the 2D electrons was inferred from the electronic noise in a gold wire, connected to the 2DEG by a metallic ohmic contact. With effective screening and filtering, we demonstrate a temperature of 0.9 ± 0.1 mK, with scope for significant further improvement. This platform is a key technological step, paving the way to observing new quantum phenomena, and developing new generations of nanoelectronic devices exploiting correlated electron states
Evidence for a Spatially Modulated Superfluid Phase of <sup>3</sup>He under Confinement
In superfluid He-B confined in a slab geometry, domain walls between
regions of different order parameter orientation are predicted to be
energetically stable. Formation of the spatially-modulated superfluid stripe
phase has been proposed. We confined He in a 1.1 m high microfluidic
cavity and cooled it into the B phase at low pressure, where the stripe phase
is predicted. We measured the surface-induced order parameter distortion with
NMR, sensitive to the formation of domains. The results rule out the stripe
phase, but are consistent with 2D modulated superfluid order.Comment: 9 pages, 9 figure
Microstructuring YbRh<sub>2</sub>Si<sub>2</sub> for resistance and noise measurements down to ultra-low temperatures
The discovery of superconductivity in the quantum critical Kondo-lattice system YbRh2Si2 at an extremely low temperature of 2 mK has inspired efforts to perform high-resolution electrical resistivity measurements down to this temperature range in highly conductive materials. Here we show that control over the sample geometry by microstructuring using focused-ion-beam techniques allows to reach ultra-low temperatures and increase signal-to-noise ratios (SNRs) tenfold, without adverse effects to sample quality. In five experiments we show four-terminal sensing resistance and magnetoresistance measurements which exhibit sharp phase transitions at the Néel temperature, and Shubnikov–de-Haas (SdH) oscillations between 13 T and 18 T where we identified a new SdH frequency of 0.39 kT. The increased SNR allowed resistance fluctuation (noise) spectroscopy that would not be possible for bulk crystals, and confirmed intrinsic 1/f -type fluctuations. Under controlled strain, two thin microstructured samples exhibited a large increase of TN from 67 mK up to 188 mK while still showing clear signatures of the phase transition and SdH oscillations. Superconducting quantum interference device-based thermal noise spectroscopy measurements in a nuclear demagnetization refrigerator down to 0.95 mK, show a sharp superconducting transition at Tc=1.2 mK. These experiments demonstrate microstructuring as a powerful tool to investigate the resistance and the noise spectrum of highly conductive correlated metals over wide temperature ranges