Browsing by Author "Savin, A."
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- Broadband Continuous-Variable Entanglement Generation Using a Kerr-Free Josephson Metamaterial
A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä(2022-08) Perelshtein, M. R.; Petrovnin, K. V.; Vesterinen, V.; Hamedani Raja, S.; Lilja, I.; Will, M.; Savin, A.; Simbierowicz, S.; Jabdaraghi, R. N.; Lehtinen, J. S.; Grönberg, L.; Hassel, J.; Prunnila, M. P.; Govenius, J.; Paraoanu, G. S.; Hakonen, P. J.Entangled microwave photons form a fundamental resource for quantum information processing and sensing with continuous variables. We use a low-loss Josephson metamaterial comprising superconducting, nonlinear, asymmetric inductive elements to generate frequency-entangled photons from vacuum fluctuations at a rate of 2 giga entangled bits per second spanning over the 4-GHz bandwidth. The device is operated as a traveling-wave parametric amplifier under Kerr-relieving biasing conditions. Furthermore, we demonstrate single-mode squeezing in such devices - 3.1±0.7dB below the zero-point level at half of modulation frequency. - Broadband Continuous-Variable Entanglement Generation Using a Kerr-Free Josephson Metamaterial
A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä(2022-08-23) Perelshtein, M. R.; Petrovnin, K. V.; Vesterinen, V.; Hamedani Raja, S.; Lilja, I.; Will, M.; Savin, A.; Simbierowicz, S.; Jabdaraghi, R. N.; Lehtinen, J. S.; Grönberg, L.; Hassel, J.; Prunnila, M. P.; Govenius, J.; Paraoanu, G. S.; Hakonen, P. J.Entangled microwave photons form a fundamental resource for quantum information processing and sensing with continuous variables. We use a low-loss Josephson metamaterial comprising superconducting, nonlinear, asymmetric inductive elements to generate frequency-entangled photons from vacuum fluctuations at a rate of 2 giga entangled bits per second spanning over the 4-GHz bandwidth. The device is operated as a traveling-wave parametric amplifier under Kerr-relieving biasing conditions. Furthermore, we demonstrate single-mode squeezing in such devices - 3.1±0.7dB below the zero-point level at half of modulation frequency. - Dry demagnetization cryostat for sub-millikelvin helium experiments: Refrigeration and thermometry
School of Science | A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä(2014) Todoshchenko, I.; Kaikkonen, J.-P.; Blaauwgeers, R.; Hakonen, Pertti J.; Savin, A.We demonstrate successful “dry” refrigeration of quantum fluids down to T = 0.16 mK by using copper nuclear demagnetization stage that is pre-cooled by a pulse-tube-based dilution refrigerator. This type of refrigeration delivers a flexible and simple sub-mK solution to a variety of needs including experiments with superfluid 3He. Our central design principle was to eliminate relative vibrations between the high-field magnet and the nuclear refrigeration stage, which resulted in the minimum heat leak of Q = 4.4 nW obtained in field of 35 mT. For thermometry, we employed a quartz tuning fork immersed into liquid 3He. We show that the fork oscillator can be considered as self-calibrating in superfluid 3He at the crossover point from hydrodynamic into ballistic quasiparticle regime. - Electron–phonon heat transport and electronic thermal conductivity in heavily doped silicon-on-insulator film
School of Science | A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä(2003) Kivinen, P.; Savin, A.; Zgirski, M.; Törmä, P.; Pekola, Jukka P.; Prunnila, M.; Ahopelto, J.Electron–phonon interaction and electronic thermal conductivity have been investigated in heavily doped silicon at subKelvin temperatures. The heat flow between electron and phonon systems is found to be proportional to T6. Utilization of a superconductor–semiconductor–superconductor thermometer enables a precise measurement of electron and substrate temperatures. The electronic thermal conductivity is consistent with the Wiedemann–Franz law. - Evidence for Magnetic Crystallization Waves at the Surface of 3He Crystal
A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä(2024-10) Todoshchenko, I.; Savin, A.; Hakonen, P. J.Ultralow temperature crystals of the helium isotopes 3He and 4He are intriguing quantum systems. Deciphering the complex features of these unusual materials has been made possible in large part by Alexander Andreev’s groundbreaking research. In 1978, Andreev and Alexander Parshin predicted the existence of melting/freezing waves at the surface of a solid 4He crystal, which was subsequently promptly detected. Successively, for the fermionic 3He superfluid/solid interface, even more intricate crystallization waves were anticipated, although they have not been observed experimentally so far. In this work, we provide preliminary results on 3He crystals at the temperature T=0.41 mK, supporting the existence of spin supercurrents in the melting/freezing waves on the crystal surface below the antiferromagnetic ordering temperature TN=0.93 mK, as predicted by Andreev. The spin currents that accompany such a melting-freezing wave make it a unique object, in which the inertial mass is distinctly different from the gravitational mass. - Flipping-Coin Experiment to Study Switching in Josephson Junctions and Superconducting Wires
A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä(2019-05-24) Zgirski, M.; Foltyn, M.; Savin, A.; Norowski, K.When probed with current pulses, Josephson junctions and superconducting wires exhibit stochastic switching from a superconducting to a stable nonzero-voltage state. The electrical current dependence of the switching probability (the so-called S curve) or the switching-current distribution is a fingerprint of the physics governing the escape process. This work addresses the criterion of the independent switching event, which is important for the credibility of the switching measurements of superconducting wires and various Josephson junctions involving superconductor-insulator-superconductor tunnel junctions, proximity junctions, and Dayem nanobridges. Treating the Josephson junction as an electrical coin with a current-tuned switching probability, we investigate the effect of correlation between switching events on the switching statistics. We show that such a correlation originates from the thermal dynamics of the superconducting wire. - Growth mode-dependent ferromagnetic properties of palladium nanoclusters
A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä(2018-07-21) Venäläinen, A.; Jalkanen, P.; Tuboltsev, V.; Savin, A.; Räisänen, J.Cluster deposited Pd films exhibit ferromagnetism in the temperature range from 1.8 to 400 K. The magnetization properties are found to be dependent on the film thickness. The varying morphology of the resulting Pd film with respect to thickness suggests that cluster size, deposition energy, and substrate type are crucial for the resulting film magnetization. This is demonstrated by the characteristic ferromagnetic hysteresis with the temperature dependent saturation magnetization, remanence, and coercivity of palladium nanocluster aggregates. The temperature dependence of the saturation magnetization, remanence, and coercivity of Pd nanoclusters were measured using an ultra-high-sensitive magnetometer based on a superconducting quantum interference device, and the morphology of the samples was analyzed by tunneling electron microscopy. - Heat Hunting in a Freezer
A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä(2020-10) Zgirski, M.; Foltyn, M.; Savin, A.; Naumov, A.; Norowski, K.Propagation and relaxation of nonequilibrium quasiparticles in superconductors are fundamental for functioning of numerous nanoscale devices, enabling operation of some of them, and limiting the performance of others. The quasiparticles heated above lattice temperature may relax locally via phonon or photon-emission channels, or diffuse over appreciable distances in a nanostructure altering the functionality of their remote components. Tracing quasiparticles experimentally in real-time domain has remained a challenging task owing to their rapid dynamics. With electronic nanothermometry, based on probing of the temperature-dependent switching current of a superconducting nanobridge, we monitor heat pulse carried by a flux of nonequilibrium quasiparticles as it passes by our detector with a noise-equivalent temperature of 10 mK/N, where N is the number of pulses probing the bridge (typically N=10000), and temporal resolution of a single nanosecond. The measurement provides the picture of quasiparticle diffusionin a superconducting aluminum strip and direct determination of the diffusion constant D equal to 100 cm2/s with no energy dependence visible. - Nanosecond Thermometry with Josephson Junctions
A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä(2018-10-29) Zgirski, M.; Foltyn, M.; Savin, A.; Norowski, K.; Meschke, M.; Pekola, J.We demonstrate a new paradigm in nanoscale thermometry exploiting well-known switching measurements of a superconducting weak link. Such a weak link probed with nanosecond current pulses serves as a temperature-sensing element and, because of the fast inherent dynamics, is capable of delivering unprecedented temporal resolution. We use the thermometer to measure the dynamic temperature of electrons in a long superconducting wire relaxing to the bath temperature after application of a heating pulse, involving evaluation of the retrapping time. Our measurement delivers resolution better than 10 ns, with potential for further improvement. It extends the temporal resolution of existing experiments and introduces new possibilities for investigating thermodynamics at the nanoscale. - Nonlocal thermoelectricity in a hybrid superconducting graphene device
A4 Artikkeli konferenssijulkaisussa(2021-06-16) Golubev, D. S.; Kirsanov, N. S.; Tan, Z. B.; Laitinen, A.; Galda, A.; Vinokur, V. M.; Haque, M.; Savin, A.; Lesovik, G. B.; Hakonen, P. J.The Seebeck effect producing voltage difference from temperature gradient has a wide spectrum of applications. Recent theoretical studies show that the Cooper pair splitting and the elastic co-tunneling can give rise to the nonlocal Seebeck effect in hybrid normal metal-superconductor-normal metal systems. Here we propose a coherent transport description of this nonlocal effect and validate its experimental observation in a graphene-based Cooper pair splitter. - Quantum degeneracy in mesoscopic matter : Casimir effect and Bose-Einstein condensation
A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä(2024-06-01) Todoshchenko, I.; Kamada, M.; Kaikkonen, J. P.; Liao, Y.; Savin, A.; Kauppinen, E.; Sergeicheva, E.; Hakonen, P. J.The ground-state phonon pressure is an analog to the famous Casimir pressure of vacuum produced by zero-point photons. The acoustic Casimir forces are, however, many orders of magnitude weaker than the electromagnetic Casimir forces, as the typical speed of sound is 100 000 times smaller than the speed of light. Because of its weakness, zero-point acoustic Casimir pressure was never observed, although the pressure of artificially introduced sound noise on a narrow aperture has been reported. However, the magnitude of Casimir pressure increases as 1/L3 with the decrease of the sample size L, and reaches piconewtons in the submicron scales. We demonstrate and measure the acoustic Casimir pressure induced by zero-point phonons in solid helium adsorbed on a carbon nanotube. We have also observed Casimir-like "pushing out"thermal phonons with the decreasing temperature or the length. We also show that all thermodynamic quantities are size dependent, and therefore in the mesoscopic range L≲h c/(kBT) quadruple points are possible on the phase diagram where four different phases coexist. Due to the smallness of solid helium sample, temperature of Bose-Einstein condensation (BEC) of vacancies is relatively high, 10-100mK. This allowed us to experimentally discover the BEC in a system of zero-point vacancies, predicted more than 50 years ago. - Quartz tuning fork as a probe of surface oscillations
A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä(2017-02-13) Todoshchenko, I.; Savin, A.; Haataja, M.; Kaikkonen, J. P.; Hakonen, P. J.Quartz tuning forks are high-quality mechanical oscillators widely used in low temperature physics as viscometers, thermometers, and pressure sensors. We demonstrate that a fork placed in liquid helium near the surface of solid helium is very sensitive to the oscillations of the solid-liquid interface. We developed a double-resonance read-out technique, which allowed us to detect oscillations of the surface with an accuracy of 1 Å in 10 s. Using this technique, we have investigated crystallization waves in 4He down to 10 mK. In contrast to previous studies of crystallization waves, our measurement scheme has very low dissipation, on the order of 20 pW, which allows us to carry out experiments even at sub-mK temperatures. We propose to use this scheme in the search for crystallization waves in 3He, which exist only at temperatures well below 0.5 mK. The suggested technique can also be used for accurate displacement detection in a large variety of systems. - Silicon-based Coulomb blockade thermometer with Schottky barriers
A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä(2014) Tuboltsev, V.; Savin, A.; Rogozin, V.D.; Raisanen, J. - Spectroscopy of Oscillation Modes in Homogeneously Precessing Domain of Superfluid 3He-B
A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä(2024-03) Zavjalov, V. V.; Savin, A.; Sergeicheva, E.; Hakonen, P. J.We study the homogeneously precessing domain (HPD) in superfluid 3He-B in a regular continuous-wave nuclear magnetic resonance (CW NMR) experiment. Using Fourier analysis of CW NMR time traces, we identify several oscillation modes with frequency monotonically increasing with the frequency shift of the HPD. Some of these modes are localized near the cell walls, while others are localized in bulk liquid and can be interpreted as oscillations of ϑ-solitons. We also observe chaotic motion of the HPD in a certain range of temperatures and frequency shifts. - Stochastic thermal feedback in switching measurements of a superconducting nanobridge caused by overheated electrons and phonons
A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä(2021-07-14) Zgirski, M.; Foltyn, M.; Savin, A.; Norowski, K.We study correlated switchings of a superconducting nanobridge probed with a train of current pulses. For pulses with a low repetition rate each pulse transits the superconducting bridge to the normal state with probability independent of the outcomes in the preceding pulses. We show that with the reduction of the time interval between pulses long-range correlation between pulses occurs: stochastic switching in a single pulse raises the temperature of the bridge and affects the outcome of the probing for the next pulses. As a result, an artificial intricate stochastic process with an adjustable strength of correlation is produced. We identify the regime where apparent switching probability exhibits the thermal hysteresis with discontinuity at a critical current amplitude of the probing pulse. This engineered stochastic process can be viewed as an artificial phase transition and provides an interesting framework for studying correlated systems. The process resembles the familiar transition from the superconducting to normal state in the current-bias nanowire, proceeding through a phase slip avalanche. Due to its extreme sensitivity to the control parameter, i.e., electric current, temperature, or magnetic field, it offers the opportunity for ultrasensitive detection. - Thermoelectric current in a graphene Cooper pair splitter
A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä(2021-12) Tan, Z. B.; Laitinen, A.; Kirsanov, N. S.; Galda, A.; Vinokur, V. M.; Haque, M.; Savin, A.; Golubev, D. S.; Lesovik, G. B.; Hakonen, P. J.Generation of electric voltage in a conductor by applying a temperature gradient is a fundamental phenomenon called the Seebeck effect. This effect and its inverse is widely exploited in diverse applications ranging from thermoelectric power generators to temperature sensing. Recently, a possibility of thermoelectricity arising from the interplay of the non-local Cooper pair splitting and the elastic co-tunneling in the hybrid normal metal-superconductor-normal metal structures was predicted. Here, we report the observation of the non-local Seebeck effect in a graphene-based Cooper pair splitting device comprising two quantum dots connected to an aluminum superconductor and present a theoretical description of this phenomenon. The observed non-local Seebeck effect offers an efficient tool for producing entangled electrons. - Topologically-imposed vacancies and mobile solid 3He on carbon nanotube
A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä(2022-10-05) Todoshchenko, I.; Kamada, M.; Kaikkonen, J. P.; Liao, Y.; Savin, A.; Will, M.; Sergeicheva, E.; Abhilash, T. S.; Kauppinen, E.; Hakonen, P. J.Low dimensional fermionic quantum systems are exceptionally interesting because they reveal distinctive physical phenomena, including among others, topologically protected excitations, edge states, frustration, and fractionalization. Our aim was to confine 3He on a suspended carbon nanotube to form 2-dimensional Fermi-system. Here we report our measurements of the mechanical resonance of the nanotube with adsorbed sub-monolayer down to 10 mK. At intermediate coverages we have observed the famous 1/3 commensurate solid. However, at larger monolayer densities we have observed a quantum phase transition from 1/3 solid to an unknown, soft, and mobile solid phase. We interpret this mobile solid phase as a bosonic commensurate crystal consisting of helium dimers with topologically-induced zero-point vacancies which are delocalized at low temperatures. We thus demonstrate that 3He on a nanotube merges both fermionic and bosonic phenomena, with a quantum phase transition between fermionic solid 1/3 phase and the observed bosonic dimer solid.