Browsing by Author "Govenius, Joonas"

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  • Bolometer operating at the threshold for circuit quantum electrodynamics
    (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
     A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
    Radiation 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.
  • Flux-tunable phase shifter for microwaves
    (2017-11-07) Kokkoniemi, Roope; Ollikainen, Tuomas; Lake, Russell; Saarenpää, Sakari; Tan, Kuan; Kokkala, Janne; Dağ, Ceren B.; Govenius, Joonas; Möttönen, Mikko
     A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
    We introduce a magnetic-flux-tunable phase shifter for propagating microwave photons, based on three equidistant superconducting quantum interference devices (SQUIDs) on a transmission line. We experimentally implement the phase shifter and demonstrate that it produces a broad range of phase shifts and full transmission within the experimental uncertainty. Together with previously demonstrated beam splitters, this phase shifter can be utilized to implement arbitrary single-qubit gates for qubits based on propagating microwave photons. These results complement previous demonstrations of on-demand single-photon sources and detectors, and hence assist in the pursuit of an all-microwave quantum computer based on propagating photons.
  • Microwave Admittance of Gold-Palladium Nanowires with Proximity-Induced Superconductivity
    (2017) Lake, Russell E.; Govenius, Joonas; Kokkoniemi, Roope; Tan, Kuan Yen; Partanen, Matti; Virtanen, Pauli; Möttönen, Mikko
     A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
    Quantitative electrical admittance measurements of diffusive superconductor-normal-metal-superconductor (SNS) junctions at gigahertz frequencies and millikelvin temperatures are reported. The gold-palladium-based SNS junctions are arranged into a chain of superconducting quantum interference devices. The chain is coupled strongly to a multimode microwave resonator with a mode spacing of approximately 0.6 GHz. By measuring the resonance frequencies and quality factors of the resonator modes, the dissipative and reactive parts of the admittance of the chain are extracted. The phase and temperature dependence of the admittance near 1 GHz are compared with theory based on the time-dependent Usadel equations. This comparison allows the identification of important discrepancies between theory and experiment that are not resolved by including inelastic scattering or elastic spin-flip scattering in the theory.
  • Nanobolometer with ultralow noise equivalent power
    (2019-10-11) Kokkoniemi, Roope; Govenius, Joonas; Vesterinen, Visa; Lake, Russell E.; Gunyho, Andras M.; Tan, Kuan Y.; Simbierowicz, Slawomir; Gronberg, Leif; Lehtinen, Janne; Prunnila, Mika; Hassel, Juha; Lamminen, Antti; Saira, Olli-Pentti; Mottonen, Mikko
     A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
    Since the introduction of bolometers more than a century ago, they have been used in various applications ranging from chemical sensors, consumer electronics, and security to particle physics and astronomy. However, faster bolometers with lower noise are of great interest from the fundamental point of view and to find new use-cases for this versatile concept. We demonstrate a nanobolometer that exhibits roughly an order of magnitude lower noise equivalent power, 20zW/root Hzp, than previously reported for any bolometer. Importantly, it is more than an order of magnitude faster than other low-noise bolometers, with a time constant of 30 mu s at 60zW/root Hzp. These results suggest a calorimetric energy resolution of 0.3 zJ = h x 0.4 THz with a time constant of 30 mu s. Further development of this nanobolometer may render it a promising candidate for future applications requiring extremely low noise and high speed such as those in quantum technology and terahertz photon counting.
  • Observation of microwave absorption and emission from incoherent electron tunneling through a normal-metal-insulator-superconductor junction
    (2018-12-01) Masuda, Shumpei; Tan, Kuan Y.; Partanen, Matti; Lake, Russell E.; Govenius, Joonas; Silveri, Matti; Grabert, Hermann; Möttönen, Mikko
     A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
    We experimentally study nanoscale normal-metal-insulator-superconductor junctions coupled to a superconducting microwave resonator. We observe that bias-voltage-controllable single-electron tunneling through the junctions gives rise to a direct conversion between the electrostatic energy and that of microwave photons. The measured power spectral density of the microwave radiation emitted by the resonator exceeds at high bias voltages that of an equivalent single-mode radiation source at 2.5 K although the phonon and electron reservoirs are at subkelvin temperatures. Measurements of the generated power quantitatively agree with a theoretical model in a wide range of bias voltages. Thus, we have developed a microwave source which is compatible with low-temperature electronics and offers convenient in-situ electrical control of the incoherent photon emission rate with a predetermined frequency, without relying on intrinsic voltage fluctuations of heated normal-metal components or suffering from unwanted losses in room temperature cables. Importantly, our observation of negative generated power at relatively low bias voltages provides a novel type of verification of the working principles of the recently discovered quantum-circuit refrigerator.
  • Parity measurement of remote qubits using dispersive coupling and photodetection
    (2015) Govenius, Joonas; Matsuzaki, Y.; Savenko, I.G.; Möttönen, Mikko
     A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
    Parity measurement is a key step in many entanglement generation and quantum error correction schemes. We propose a protocol for nondestructive parity measurement of two remote qubits, i.e., macroscopically separated qubits with no direct interaction. The qubits are instead dispersively coupled to separate resonators that radiate to shared photodetectors. The scheme is deterministic in the sense that there is no fundamental upper bound on the success probability. In contrast to previous proposals, our protocol addresses the scenario where number-resolving photodetectors are available but the qubit-resonator coupling is time independent and only dispersive.
  • Propagating quantum microwaves : towards applications in communication and sensing
    (2023-04) Casariego, Mateo; Zambrini Cruzeiro, Emmanuel; Gherardini, Stefano; Gonzalez-Raya, Tasio; André, Rui; Frazão, Gonçalo; Catto, Giacomo; Möttönen, Mikko; Datta, Debopam; Viisanen, Klaara; Govenius, Joonas; Prunnila, Mika; Tuominen, Kimmo; Reichert, Maximilian; Renger, Michael; Fedorov, Kirill G.; Deppe, Frank; van der Vliet, Harriet; Matthews, A. J.; Fernández, Yolanda; Assouly, R.; Dassonneville, R.; Huard, B.; Sanz, Mikel; Omar, Yasser
     A2 Katsausartikkeli tieteellisessä aikakauslehdessä
    The field of propagating quantum microwaves is a relatively new area of research that is receiving increased attention due to its promising technological applications, both in communication and sensing. While formally similar to quantum optics, some key elements required by the aim of having a controllable quantum microwave interface are still on an early stage of development. Here, we argue where and why a fully operative toolbox for propagating quantum microwaves will be needed, pointing to novel directions of research along the way: from microwave quantum key distribution to quantum radar, bath-system learning, or direct dark matter detection. The article therefore functions both as a review of the state-of-the-art, and as an illustration of the wide reach of applications the future of quantum microwaves will open.
  • Quantum-circuit Refrigerator
    (2017-05-08) Tan, Kuan; Partanen, Matti; Lake, Russell; Govenius, Joonas; Masuda, Shumpei; Möttönen, Mikko
     A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
    Quantum technology promises revolutionizing applications in information processing, communications, sensing and modelling. However, efficient on-demand cooling of the functional quantum degrees of freedom remains challenging in many solid-state implementations, such as superconducting circuits. Here we demonstrate direct cooling of a superconducting resonator mode using voltage-controllable electron tunnelling in a nanoscale refrigerator. This result is revealed by a decreased electron temperature at a resonator-coupled probe resistor, even for an elevated electron temperature at the refrigerator. Our conclusions are verified by control experiments and by a good quantitative agreement between theory and experimental observations at various operation voltages and bath temperatures. In the future, we aim to remove spurious dissipation introduced by our refrigerator and to decrease the operational temperature. Such an ideal quantum-circuit refrigerator has potential applications in the initialization of quantum electric devices. In the superconducting quantum computer, for example, fast and accurate reset of the quantum memory is needed.
  • Towards calorimetric detection of individual itinerant microwave photons
    (2016) Govenius, Joonas
     School of Science | Doctoral dissertation (article-based)
    This dissertation focuses on the development of a new type of thermal microwave photodetector based on superconductor–normal-metal–superconductor (SNS) junctions.  We motivate the development of the detector mainly by microwave quantum optics applications in the context of superconducting qubits coupled to microwave transmission lines and resonators, i.e., in the context of circuit quantum electrodynamics (cQED). In cQED, single-photon microwave pulses naturally arise as a results of a qubit exchanging its excitation with a transmission line. While immense progress has been achieved in cQED in general, and in linear microwave amplification in particular, the challenge of developing an efficient and practical detector for single itinerant photons remains open, mostly due to the exceedingly small energy of individual microwave photons. This prevents microwave implementations of a certain class of quantum optical protocols, including the parity measurement protocol proposed in this dissertation.  The core of this dissertation is dedicated to introducing our detector design, discussing the thermal properties of the detector in detail, and demonstrating the operation of the detector in a time-gated threshold detection mode. In particular, we demonstrate threshold detection of coherent 8.4 GHz microwave pulses containing roughly 200 photons, or 1.1 zJ of energy. Compared to other thermal detectors, this is an order of magnitude improvement in the energy of the detected pulses.  In addition, we characterize the linear response of the SNS junctions as separate components. That is, we embed the junctions in a microwave circuit that is specifically designed to allow determining the electrical admittance of the SNS junctions from the response of the circuit as a whole.