Browsing by Author "Hassel, J."

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  • Broadband Continuous-Variable Entanglement Generation Using a Kerr-Free Josephson Metamaterial
    (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.
     A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
    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
    (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.
     A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
    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.
  • Control of Coulomb blockade in a mesoscopic Josephson junction using single electron tunneling
    (2004) Hassel, J.; Seppä, Heikki; Delahaye, Julien; Hakonen, Pertti J.
     School of Science | A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
    We study a circuit where a mesoscopic Josephson junction(JJ) is embedded in an environment consisting of a large bias resistor and a normal-insulator-superconductor (NIS) junction. The effective Coulomb blockade of the JJ can be controlled by the tunneling current through the NIS junction leading to transistor-like characteristics. We show using phase correlation theory and numerical simulations that substantial current gain with low current noise (in≲1 fA/√Hz) and noise temperature (≲0.1 K) can be achieved. Good agreement between our numerical simulations and experimental results is obtained.
  • Flux-tunable heat sink for quantum electric circuits
    (2018-12-01) Partanen, M.; Tan, K. Y.; Masuda, S.; Govenius, J.; Lake, R. E.; Jenei, M.; Grönberg, L.; Hassel, J.; Simbierowicz, S.; Vesterinen, V.; Tuorila, J.; Ala-Nissila, T.; Möttönen, M.
     A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
    Superconducting microwave circuits show great potential for practical quantum technological applications such as quantum information processing. However, fast and on-demand initialization of the quantum degrees of freedom in these devices remains a challenge. Here, we experimentally implement a tunable heat sink that is potentially suitable for the initialization of superconducting qubits. Our device consists of two coupled resonators. The first resonator has a high quality factor and a fixed frequency whereas the second resonator is designed to have a low quality factor and a tunable resonance frequency. We engineer the low quality factor using an on-chip resistor and the frequency tunability using a superconducting quantum interference device. When the two resonators are in resonance, the photons in the high-quality resonator can be efficiently dissipated. We show that the corresponding loaded quality factor can be tuned from above 105 down to a few thousand at 10 GHz in good quantitative agreement with our theoretical model.
  • High-resolution superconducting single-flux quantum comparator for sub-Kelvin temperatures
    (2006) Savin, A. M.; Pekola, Jukka P.; Holmqvist, T.; Hassel, J.; Grönberg, L.; Helistö, P.; Kidiyarova-Shevchenko, A.
     School of Science | A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
    A design of sub-Kelvin single-flux quantum (SFQ) circuits with reduced power dissipation and additional cooling of shunt resistors has been developed and characterized. The authors demonstrate operation of SFQ comparators with current resolution of 40nA at 2GHz sampling rate. Due to improved cooling the electron temperature in shunt resistors of a SFQ comparator is below 50mK when the bath temperature is about 30mK.
  • Initial experimental results on a superconducting-qubit reset based on photon-assisted quasiparticle tunneling
    (2022-12-07) Sevriuk, V.A.; Liu, W.; Rönkkö, J.; Hsu, H.; Marxer, F.; Mörstedt, T.F.; Partanen, M.; Räbinä, J.; Venkatesh, M.; Hotari, J.; Grönberg, L.; Heinsoo, J.; Li, T.; Tuorila, J.; Chan, K.W.; Hassel, J.; Tan, K.Y.; Möttönen, M.
     A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
    We present here our recent results on qubit reset scheme based on a quantum-circuit refrigerator (QCR). In particular, we use the photon-assisted quasiparticle tunneling through a superconductor–insulator–normal-metal–insulator–superconductor junction to controllably decrease the energy relaxation time of the qubit during the QCR operation. In our experiment, we use a transmon qubit with dispersive readout. The QCR is capacitively coupled to the qubit through its normal-metal island. We employ rapid, square-shaped QCR control voltage pulses with durations in the range of 2–350 ns and a variety of amplitudes to optimize the reset time and fidelity. Consequently, we reach a qubit ground-state probability of roughly 97% with 80-ns pulses starting from the first excited state. The qubit state probability is extracted from averaged readout signal, where the calibration is based on Rabi oscillations, thus not distinguishing the residual thermal population of the qubit.
  • Low Noise Current Amplifier Based on Mesoscopic Josephson Junction
    (2003) Delahaye, Julien; Hassel, J.; Lindell, Rene; Sillanpää, Mika; Paalanen, Mikko; Seppä, Heikki; Hakonen, Pertti J.
     School of Science | A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
    We utilize the band structure of a mesoscopic Josephson junction to construct low noise amplifiers. By taking advantage of the quantum dynamics of a Josephson junction, i.e. the interplay of interlevel transitions and the Coulomb blockade of Cooper pairs, we create transistor-like devices, Bloch oscillating transistors, with considerable current gain and high input impedance. In these transistors, correlated supercurrent of Cooper pairs is controlled by a small base current made of single electrons. Our devices reach current and power gains on the order of 30 and 5, respectively. The noise temperature is estimated to be around 1 Kelvin, but it is realistic to achieve TN < 0.1 Kelvin. These devices provide quantum-electronic building blocks that will be useful in low-noise, intermediate-impedance-level circuit applications at low temperatures.