Browsing by Author "Hakonen, Pertti J."
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Item Accessing nanomechanical resonators via a fast microwave circuit(AIP Publishing, 2009) Sillanpää, Mika A.; Sarkar, Jayanta; Sulkko, Jaakko; Muhonen, Juha; Hakonen, Pertti J.; Teknillisen fysiikan laitos; Department of Applied Physics; Perustieteiden korkeakoulu; School of ScienceWe demonstrate how to fully electrically detect the vibrations of conductive nanomechanical resonators up to the microwave regime. We use the electrically actuated vibrations to modulate an LC tank circuit, which blocks the stray capacitance and detect the created sideband voltage by a microwave analyzer. We prove the technique up to mechanical frequencies of 200 MHz. Finally, we estimate how one could approach the quantum limit of mechanical systems.Item Autler-Townes Effect in a Superconducting Three-Level System(American Physical Society (APS), 2009) Sillanpää, Mika A.; Li, Jian; Cicak, Katarina; Altomare, Fabio; Park, Jae I.; Simmonds, Raymond W.; Paraoanu, G. S.; Hakonen, Pertti J.; Teknillisen fysiikan laitos; Department of Applied Physics; Perustieteiden korkeakoulu; School of ScienceWhen a three-level quantum system is irradiated by an intense coupling field resonant with one of the three possible transitions, the absorption peak of an additional probe field involving the remaining level is split. This process is known in quantum optics as the Autler-Townes effect. We observe these phenomena in a superconducting Josephson phase qubit, which can be considered an “artificial atom” with a multilevel quantum structure. The spectroscopy peaks can be explained reasonably well by a simple three-level Hamiltonian model. Simulation of a more complete model (including dissipation, higher levels, and cross coupling) provides excellent agreement with all of the experimental data.Item Bipolar programmable current supply for superconducting nuclear magnetic resonance magnets(AIP Publishing, 1998) Koivuniemi, Jaakko; Luusalo, Reeta; Hakonen, Pertti J.; Teknillisen fysiikan laitos; Department of Applied Physics; Perustieteiden korkeakoulu; School of ScienceIn high resolution continuous-wave nuclear magnetic resonance(NMR) work well-reproducible, linear sweeps of current are needed. We have developed a microcontroller based programmable current supply, tested with superconducting magnets with inductance of 10 mH and 10 H. We achieved a resolution and noise of 4 ppm. The supply has an internal sweep with programmable ramping rate and a possibility for remote operation from a computer with either GPIB or RS232 interface. It is based on an 18-bit D/A converter. The maximum output current is ±10 A, the sweep rate can be set between 1 μA/s–140 mA/s, and the maximum output voltage is ±2.5 V. In work at ultralow temperatures, especially in superconducting quantum interference device NMR, all rf interference to the experiment should be avoided. One of the sources of this kind of unwanted input is the digital switching noise of fast logic devices. We discuss this problem in the context of our design.Item Bolometer operating at the threshold for circuit quantum electrodynamics(Nature Publishing Group, 2020-10-01) Kokkoniemi, Roope; Girard, Jean-Philippe; Hazra, Dibyendu; Laitinen, Antti; Govenius, Joonas; Lake, Russell; Sallinen, Iiro; Vesterinen, Visa; Partanen, Matti; Tan, J. Y.; Chan, K.W.; Tan, Kuan; Hakonen, Pertti J.; Möttönen, Mikko; Department of Applied Physics; Centre of Excellence in Quantum Technology, QTF; Quantum Computing and Devices; Quantum Circuits and Correlations; Department of Applied Physics; National University of SingaporeRadiation sensors based on the heating effect of absorbed radiation are typically simple to operate and flexible in terms of input frequency, so they are widely used in gas detection, security, terahertz imaging, astrophysical observations and medical applications. Several important applications are currently emerging from quantum technology and especially from electrical circuits that behave quantum mechanically, that is, circuit quantum electrodynamics. This field has given rise to single-photon microwave detectors and a quantum computer that is superior to classical supercomputers for certain tasks. Thermal sensors hold potential for enhancing such devices because they do not add quantum noise and they are smaller, simpler and consume about six orders of magnitude less power than the frequently used travelling-wave parametric amplifiers. However, despite great progress in the speed and noise levels of thermal sensors, no bolometer has previously met the threshold for circuit quantum electrodynamics, which lies at a time constant of a few hundred nanoseconds and a simultaneous energy resolution of the order of 10h gigahertz (where h is the Planck constant). Here we experimentally demonstrate a bolometer that operates at this threshold, with a noise-equivalent power of 30 zeptowatts per square-root hertz, comparable to the lowest value reported so far, at a thermal time constant two orders of magnitude shorter, at 500 nanoseconds. Both of these values are measured directly on the same device, giving an accurate estimation of 30h gigahertz for the calorimetric energy resolution. These improvements stem from the use of a graphene monolayer with extremely low specific heat as the active material. The minimum observed time constant of 200 nanoseconds is well below the dephasing times of roughly 100 microseconds reported for superconducting qubits and matches the timescales of currently used readout schemes, thus enabling circuit quantum electrodynamics applications for bolometers.Item Breakdown of Zero-Energy Quantum Hall State in Graphene in the Light of Current Fluctuations and Shot Noise(2018) Laitinen, Antti; Kumar, Manohar; Elo, Teemu; Liu, Ying; Abhilash, T. S.; Hakonen, Pertti J.; Department of Applied PhysicsWe have investigated the cross-over from Zener tunneling of single charge carriers to avalanche type of bunched electron transport in a suspended graphene Corbino disk in the zeroth Landau level. At low bias, we find a tunneling current that follows the gyrotropic Zener tunneling behavior. At larger bias, we find an avalanche type of transport that sets in at a smaller current the larger the magnetic field is. The low-frequency noise indicates strong bunching of the electrons in the avalanches. On the basis of the measured low-frequency switching noise power, we deduce the characteristic switching rates of the avalanche sequence. The simultaneous microwave shot noise measurement also reveals intrinsic correlations within the avalanche pulses and indicate a decrease in correlations with increasing bias.Item Charge sensitivity of the inductive single-electron transistor(AIP Publishing, 2005) Sillanpää, Mika A.; Roschier, Leif; Hakonen, Pertti J.; Teknillisen fysiikan laitos; Department of Applied Physics; Perustieteiden korkeakoulu; School of ScienceWe calculate the charge sensitivity of a recently demonstrated device where the Josephson inductance of a single Cooper-pair transistor is measured. We find that the intrinsic limit to detector performance is set by oscillatorquantum noise. Sensitivity better than 10−6e/√Hz is possible with a high Q value ∼103, or using a superconducting quantum interference deviceamplifier. The model is compared to experiment, where charge sensitivity 3×10−5e/√Hz and bandwidth 100 MHz are achieved.Item Coherence and multimode correlations from vacuum fluctuations in a microwave superconducting cavity(2016-08-26) Lähteenmäki, Pasi; Paraoanu, Gheorghe Sorin; Hassel, Juha; Hakonen, Pertti J.; Department of Applied Physics; Superconducting Qubits and Circuit QED; Quantum Circuits and Correlations; VTT Technical Research Centre of FinlandThe existence of vacuum fluctuations is one of the most important predictions of modern quantum field theory. In the vacuum state, fluctuations occurring at different frequencies are uncorrelated. However, if a parameter in the Lagrangian of the field is modulated by an external pump, vacuum fluctuations stimulate spontaneous downconversion processes, creating squeezing between modes symmetric with respect to half of the frequency of the pump. Here we show that by double parametric pumping of a superconducting microwave cavity, it is possible to generate another type of correlation, namely coherence between photons in separate frequency modes. The coherence correlations are tunable by the phases of the pumps and are established by a quantum fluctuation that stimulates the simultaneous creation of two photon pairs. Our analysis indicates that the origin of this vacuum-induced coherence is the absence of which-way information in the frequency space.Item Comment on "Absence of a Dissipative Quantum Phase Transition in Josephson Junctions"(American Physical Society, 2021-03-12) Hakonen, Pertti J.; Sonin, Edouard B.; Centre of Excellence in Quantum Technology, QTF; Hebrew University of Jerusalem; Department of Applied PhysicsItem Comment on 'Nucleation of 3He-B from the A Phase: A Cosmic-Ray Effect?'(American Physical Society (APS), 1985) Hakonen, Pertti J.; Krusius, M.; Salomaa, M. M.; Simola, J. T.; Teknillisen fysiikan laitos; Department of Applied Physics; Perustieteiden korkeakoulu; School of ScienceA comment to the article by Leggett, A. J.Item Continuous Vortices with Broken Symmetry in Rotating Superfluid 3He-A(American Physical Society (APS), 1984) Seppälä, H. K.; Hakonen, Pertti J.; Krusius, M.; Ohmi, T.; Salomaa, M. M.; Simola, J. T.; Volovik, G. E.; Teknillisen fysiikan laitos; Department of Applied Physics; Perustieteiden korkeakoulu; School of ScienceNew NMR measurements are reported on continuous 3He-A vortices in tilted magnetic fields. We introduce a symmetry classification of the continuous vortices with broken axial symmetry. It is found that the discrete internal symmetry may in addition be broken in two inequivalent ways, producing two different continuous vortices. Although NMR may not distinguish between these two vortices, the observed vortex satellite peak is well accounted for by spin waves localized in the soft core of such vortices.Item Control of Coulomb blockade in a mesoscopic Josephson junction using single electron tunneling(AIP Publishing, 2004) Hassel, J.; Seppä, Heikki; Delahaye, Julien; Hakonen, Pertti J.; Teknillisen fysiikan laitos; Department of Applied Physics; Perustieteiden korkeakoulu; School of ScienceWe 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.Item Controlling supercurrents using single-walled carbon nanotube weak links(IOP Publishing, 2009) Wu, F.; Danneau, R.; Queipo, P.; Kauppinen, Esko I.; Tsuneta, T.; Hakonen, Pertti J.; Teknillisen fysiikan laitos; Department of Applied Physics; Perustieteiden korkeakoulu; School of ScienceWe have investigated proximity-induced supercurrents in single-walled carbon nanotubes. Phase diffusion is found to be present in the maximum measured supercurrent of 4.8 nA, which results in a minimum of 100Ω zero bias resistance in superconducting state. We also observe that the supercurrent is very sensitive to the measurement bandwidth and large phase fluctuations can even destroy the supercurrents. Our results shed light on the methods of how to improve the performance of high frequency superconducting single-walled nanotube devices.Item Cooled video camera for optical investigations below 1 mK(AIP Publishing, 1994) Alles, H.; Ruutu, J. P.; Babkin, A. V.; Hakonen, Pertti J.; Manninen, A. J.; Pekola, Jukka P.; Department of Applied Physics; Teknillisen fysiikan laitos; Perustieteiden korkeakoulu; School of ScienceAn optical imaging system for milliKelvin temperatures has been developed based on a regular B/W surveillance camera (25 frames/s), with its CCD sensor inside the 4‐K vacuum can of our nuclear demagnetization cryostat. The heat leak to the nuclear stage, caused by the operation of the video camera, was reduced below 1 nW by careful rf shielding. The construction of the system and its limits of operation are discussed.Item Cooper Pair Splitting by Means of Graphene Quantum Dots(American Physical Society (APS), 2015) Tan, Z. B.; Cox, D.; Nieminen, T.; Lähteenmäki, P.; Golubev, D.; Lesovik, G. B.; Hakonen, Pertti J.; Teknillisen fysiikan laitos; Department of Applied Physics; Perustieteiden korkeakoulu; School of ScienceA split Cooper pair is a natural source for entangled electrons which is a basic ingredient for quantum information in the solid state. We report an experiment on a superconductor-graphene double quantum dot (QD) system, in which we observe Cooper pair splitting (CPS) up to a CPS efficiency of ∼10%. With bias on both QDs, we are able to detect a positive conductance correlation across the two distinctly decoupled QDs. Furthermore, with bias only on one QD, CPS and elastic cotunneling can be distinguished by tuning the energy levels of the QDs to be asymmetric or symmetric with respect to the Fermi level in the superconductor.Item Coupling between electrons and optical phonons in suspended bilayer graphene(American Physical Society (APS), 2015) Laitinen, Antti; Kumar, Manohar; Oksanen, Mika; Placais, Bernard; Virtanen, Pauli; Hakonen, Pertti J.; Teknillisen fysiikan laitos; Department of Applied Physics; Perustieteiden korkeakoulu; School of ScienceUsing electrical transport experiments and shot noise thermometry, we investigate electron-phonon heat transfer rate in a suspended bilayer graphene. Contrary to monolayer graphene with heat flow via three-body supercollision scattering, we find that regular electron–optical-phonon scattering in bilayer graphene provides the dominant scattering process at electron energies ≳0.15 eV. We determine the strength of these intrinsic heat flow processes of bilayer graphene and find good agreement with theoretical estimates when both zone edge and zone center optical phonons are taken into account.Item Current-phase relation and Josephson inductance in a superconducting Cooper-pair transistor(American Physical Society (APS), 2009) Paila, A.; Gunnarsson, D.; Sarkar, J.; Sillanpää, Mika A.; Hakonen, Pertti J.; Teknillisen fysiikan laitos; Department of Applied Physics; Perustieteiden korkeakoulu; School of ScienceWe have investigated the Josephson inductance LJ of a superconducting Cooper pair transistor (SCPT). We traced the inductance using microwave reflection measurements on a tuned resonance circuit in which a SCPT was mounted in parallel to a ∼200 pH strip line inductance. When the inverse of the Josephson inductance, determined on the charge-phase bias plane for a SCPT with a Josephson to Coulomb energy ratio of EJ/EC=1.75, is integrated over the phase, we obtain a current-phase relation, which is strongly nonsinusoidal near the charge degeneracy point.Item Cyclostationary shot noise in mesoscopic measurements(AIP Publishing, 2004) Roschier, Leif; Heikkilä, Tero T.; Hakonen, Pertti J.; Teknillisen fysiikan laitos; Department of Applied Physics; Perustieteiden korkeakoulu; School of ScienceWe discuss theoretically a setup where a time-dependent current consisting of a dc bias and two sinusoidal harmonics is driven through a sample. If the sample exhibits current-dependent shot noise, the down-converted noise power spectrum varies depending on the local-oscillator phase of the mixer. The theory of this phase-dependent noise is applied to discuss the measurement of the radio-frequency single-electron transistor. We also show that this effect can be used to measure the shot noise accurately even in nonlinear high-impedance samples.Item Decoherence, Autler-Townes effect, and dark states in two-tone driving of a three-level superconducting system(American Physical Society (APS), 2011) Li, Jian; Paraoanu, G. S.; Cicak, Katarina; Altomare, Fabio; Park, Jae I.; Simmonds, Raymond W.; Sillanpää, Mika A.; Hakonen, Pertti J.; Teknillisen fysiikan laitos; Department of Applied Physics; Perustieteiden korkeakoulu; School of ScienceWe present a detailed theoretical analysis of a multilevel quantum system coupled to two radiation fields and subject to decoherence. We concentrate on an effect known from quantum optics as Autler-Townes splitting, which has been recently demonstrated experimentally [M. A. Sillanpää et al., Phys. Rev. Lett. 103, 193601 (2009)] in a superconducting phase qubit. In the three-level approximation, we derive analytical solutions and describe how they can be used to extract the decoherence rates and to account for the measurement data. Better agreement with the experiment can be obtained by extending this model to five levels. Finally, we investigate the stationary states created in the experiment and show that their structure is close to that of dark states.Item Design of cryogenic 700 MHz HEMT amplifier(Elsevier BV, 2004) Roschier, Leif; Hakonen, Pertti J.; Teknillisen fysiikan laitos; Department of Applied Physics; Perustieteiden korkeakoulu; School of ScienceWe present a way to design a high-frequency low-temperature pHEMT-based balanced amplifier. The design is based on measured cryogenic S-parameters combined with a small-signal noise model. Using the design process we constructed an amplifier that was measured to have a gain of 16 dB and a noise temperature of ∼3 K when cooled to 4.2 K.Item Detection of the Rotation of the Earth with a Superfluid Gyrometer(American Physical Society (APS), 1997) Avenel, O.; Hakonen, Pertti J.; Varoquaux, E.; Teknillisen fysiikan laitos; Department of Applied Physics; Perustieteiden korkeakoulu; School of ScienceThe effect of the rotation of the Earth, Ω⊕, on a superfluid resonator equipped with a 4.0 cm exp 2 rotation pickup loop and with a microaperture is reported. The velocity circulation induced in the loop by the rotation is detected by phase-slippage techniques. The magnitude of Ω⊕ is measured to better than 1%, and the north direction to ±0.5° for a 10 h observation time. This experiment is the superfluid counterpart of interferometric measurements based on the Sagnac effect.
