arXiv subjects

Olli-Pentti Saira

Publications and source records attributed to Olli-Pentti Saira.

12 recordsLinked to original sources

arXiv2022

Hot Carrier Thermalization and Josephson Inductance Thermometry in a Graphene-based Microwave Circuit

Due to its exceptional electronic and thermal properties, graphene is a key material for bolometry, calorimetry, and photon detection. However, despite graphene's relatively simple electronic structure, the physical processes responsible for the transport of heat from the electrons to the lattice are experimentally still elusive. Here, we measure the thermal response of low-disorder graphene encapsulated in hexagonal boron nitride (hBN) by integrating it within a multi-terminal superconducting device coupled to a microwave resonator. This technique allows us to simultaneously apply Joule heat power to the graphene flake while performing calibrated readout of the electron temperature. We probe the thermalization rates of both electrons and holes with high precision and observe a thermalization scaling exponent consistent with cooling dominated by resonant electron-phonon coupling processes occurring at the interface between graphene and superconducting leads. The technique utilized here is applicable for wide range of semiconducting-superconducting interface heterostructures and provides new insights into the thermalization pathways essential for the next-generation thermal detectors.

cond-mat.mes-hall↗

arXiv2019

Modification of electron-phonon coupling by micromachining and suspension

Weak electron-phonon interaction in metals at low temperatures forms the basis of operation for cryogenic hot-electron bolometers and calorimeters. Standard power laws, describing the heat flow in the majority of experiments, have been identified and derived theoretically. However, a full picture encompassing experimentally relevant effects such as reduced dimensionality, material interfaces, and disorder is in its infancy, and has not been tested extensively. Here, we study the electron-phonon heat flow in a thin gold film on a SiO${}_2$ platform below 100 mK using supercurrent thermometry. We find the power law exponent to be modified from 5.1 to 4.6 as the platform is micromachined and released from its substrate. We attribute this change to a modified phonon spectrum. The findings are compared to past experiments and theoretical models.

cond-mat.mes-hall↗

arXiv2019

Nonequilibrium thermodynamics of erasure with superconducting flux logic

We implement a thermal-fluctuation driven logical bit reset on a superconducting flux logic cell. We show that the logical state of the system can be continuously monitored with only a small perturbation to the thermally activated dynamics at 500 mK. We use the trajectory information to derive a single-shot estimate of the work performed on the system per logical cycle. We acquire a sample of $10^5$ erasure trajectories per protocol, and show that the work histograms agree with both microscopic theory and global fluctuation theorems. The results demonstrate how to design and diagnose complex, high-speed, and thermodynamically efficient computing using superconducting technology.

cond-mat.mes-hall↗

arXiv2019

Harnessing Fluctuations in Thermodynamic Computing via Time-Reversal Symmetries

We experimentally demonstrate that highly structured distributions of work emerge during even the simple task of erasing a single bit. These are signatures of a refined suite of time-reversal symmetries in distinct functional classes of microscopic trajectories. As a consequence, we introduce a broad family of conditional fluctuation theorems that the component work distributions must satisfy. Since they identify entropy production, the component work distributions encode both the frequency of various mechanisms of success and failure during computing, as well giving improved estimates of the total irreversibly-dissipated heat. This new diagnostic tool provides strong evidence that thermodynamic computing at the nanoscale can be constructively harnessed. We experimentally verify this functional decomposition and the new class of fluctuation theorems by measuring transitions between flux states in a superconducting circuit.

cond-mat.stat-mech↗

arXiv2017

Fast thermometry with a proximity Josephson junction

We couple a proximity Josephson junction to a Joule-heated normal metal film and measure its electron temperature under steady state and nonequilibrium conditions. With a timed sequence of heating and temperature probing pulses, we are able to monitor its electron temperature in nonequilibrium with effectively zero back-action from the temperature measurement in the form of additional dissipation or thermal conductance. The experiments demonstrate the possibility of using a fast proximity Josephson junction thermometer for studying thermal transport in mesoscopic systems and for calorimetry.

cond-mat.mes-hall↗

arXiv2014

Incomplete measurement of work in a dissipative two level system

We discuss work performed on a quantum two-level system coupled to multiple thermal baths. To evaluate the work, a measurement of photon exchange between the system and the baths is envisioned. In a realistic scenario, some photons remain unrecorded as they are exchanged with baths that are not accessible to the measurement, and thus only partial information on work and heat is available. The incompleteness of the measurement leads to substantial deviations from standard fluctuation relations. We propose a recovery of these relations, based on including the mutual information given by the counting efficiency of the partial measurement. We further present the experimental status of a possible implementation of the proposed scheme, i.e. a calorimetric measurement of work, currently with nearly single-photon sensitivity.

cond-mat.stat-mech↗

arXiv2010

Single-charge escape processes through a hybrid turnstile in a dissipative environment

We have investigated the static, charge-trapping properties of a hybrid superconductor---normal metal electron turnstile embedded into a high-ohmic environment. The device includes a local Cr resistor on one side of the turnstile, and a superconducting trapping island on the other side. The electron hold times, t ~ 2-20s, in our two-junction circuit are comparable with those of typical multi-junction, N >= 4, normal-metal single-electron tunneling devices. A semi-phenomenological model of the environmental activation of tunneling is applied for the analysis of the switching statistics. The experimental results are promising for electrical metrology.

cond-mat.supr-con↗

arXiv2007

Hybrid single-electron transistor as a source of quantized electric current

The basis of synchronous manipulation of individual electrons in solid-state devices was laid by the rise of single-electronics about two decades ago. Ultra-small structures in a low temperature environment form an ideal domain of addressing electrons one by one. A long-standing challenge in this field has been the realization of a source of electric current that is accurately related to the operation frequency $f$. There is an urgent call for a quantum standard of electric current and for the so-called metrological triangle, where voltage from Josephson effect and resistance from quantum Hall effect are tested against current via Ohm's law for a consistency check of the fundamental constants of Nature, $\hbar$ and $e$. Several attempts to create a metrological current source that would comply with the demanding criteria of extreme accuracy, high yield, and implementation with not too many control parameters have been reported. However, no satisfactory solution exists as yet despite many ingenious achievements that have been witnessed over the years. Here we propose and prove the unexpected concept of a hybrid metal-superconductor turnstile in the form of a one-island single-electron transistor with one gate, which demonstrates robust current plateaus at multiple levels of $ef$ within the uncertainty of our current measurement. Our theoretical estimates show that the errors of the present system can be efficiently suppressed by further optimizations of design and proper choice of the device parameters and therefore we expect it to eventually meet the stringent specifications of quantum metrology.

cond-mat.mes-hall↗

arXiv2007

Suppression of 1/f noise in one-qubit systems

We investigate the generation of quantum operations for one-qubit systems under classical noise with 1/f^αpower spectrum, where 2>α> 0. We present an efficient way to approximate the noise with a discrete multi-state Markovian fluctuator. With this method, the average temporal evolution of the qubit density matrix under 1/f^αnoise can be feasibly determined from recently derived deterministic master equations. We obtain qubit operations such as quantum memory and the NOT}gate to high fidelity by a gradient based optimization algorithm. For the NOT gate, the computed fidelities are qualitatively similar to those obtained earlier for random telegraph noise. In the case of quantum memory however, we observe a nonmonotonic dependency of the fidelity on the operation time, yielding a natural access rate of the memory.

quant-ph↗

arXiv2007

Equivalent qubit dynamics under classical and quantum noise

We study the dynamics of quantum systems under classical and quantum noise, focusing on decoherence in qubit systems. Classical noise is described by a random process leading to a stochastic temporal evolution of a closed quantum system, whereas quantum noise originates from the coupling of the microscopic quantum system to its macroscopic environment. We derive deterministic master equations describing the average evolution of the quantum system under classical continuous-time Markovian noise and two sets of master equations under quantum noise. Strikingly, these three equations of motion are shown to be equivalent in the case of classical random telegraph noise and proper quantum environments. Hence fully quantum-mechanical models within the Born approximation can be mapped to a quantum system under classical noise. Furthermore, we apply the derived equations together with pulse optimization techniques to achieve high-fidelity one-qubit operations under random telegraph noise, and hence fight decoherence in these systems of great practical interest.

quant-ph↗

arXiv2007

Heat Transistor: Demonstration of Gate-Controlled Electron Refrigeration

We present experiments on a superconductor-normal metal electron refrigerator in a regime where single-electron charging effects are significant. The system functions as a heat transistor, i.e., the heat flux out from the normal metal island can be controlled with a gate voltage. A theoretical model developed within the framework of single-electron tunneling provides a full quantitative agreement with the experiment. This work serves as the first experimental observation of Coulombic control of heat transfer and, in particular, of refrigeration in a mesoscopic system.

cond-mat.mes-hall↗

arXiv2006

Radio-Frequency Single-Electron Refrigerator

We propose a cyclic refrigeration principle based on mesoscopic electron transport. Synchronous sequential tunnelling of electrons in a Coulomb-blockaded device, a normal metal-superconductor single-electron box, results in a cooling power of $\sim k_{\rm B}T \times f$ at temperature $T$ over a wide range of cycle frequencies $f$. Electrostatic work, done by the gate voltage source, removes heat from the Coulomb island with an efficiency of $\sim k_{\rm B}T/Δ$, where $Δ$ is the superconducting gap. The performance is not affected significantly by non-idealities, for instance by offset charges. We propose ways of characterizing the system and of its practical implementation.

cond-mat.mes-hall↗