arXiv subjects

Máté Jenei

Publications and source records attributed to Máté Jenei.

8 recordsLinked to original sources

arXiv2021

Photon-number-dependent effective Lamb shift

The Lamb shift, an energy shift arising from the presence of the electromagnetic vacuum, has been observed in various quantum systems and established as the part of the energy shift independent of the environmental photon number. However, typical studies are based on simplistic bosonic models which may be challenged in practical quantum devices. We demonstrate a hybrid bosonic-fermionic environment for a linear resonator mode and observe that the photon number in the environment can dramatically increase both the dissipation and the effective Lamb shift of the mode. Our observations are quantitatively described by a first-principles model which we develop here also to guide device design for future quantum-technological applications. The device demonstrated here can be utilized as a fully rf-operated quantum-circuit refrigerator to quickly reset superconducting qubits.

quant-ph↗

arXiv2020

Realisation of a quantum current standard at liquid helium temperature with sub-ppm reproducibility

A silicon electron pump operating at the temperature of liquid helium has demonstrated repeatable operation with sub-ppm accuracy. The pump current, approximately 168 pA, is measured by three laboratories, and the measurements agree with the expected current ef within the uncertainties which range from 0.2 ppm to 1.3 ppm. All the measurements are carried out in zero applied magnetic field, and the pump drive signal is a sine wave. The combination of simple operating conditions with high accuracy demonstrates the possibility that an electron pump can operate as a current standard in a National Measurement Institute. We also discuss other practical aspects of using the electron pump as a current standard, such as testing its robustness to changes in the control parameters, and using a rapid tuning procedure to locate the optimal operation point..

physics.ins-det↗

arXiv2019

Superconducting charge sensor coupled to an electron layer in silicon

Schemes aimed at transferring individual electrons in semiconductor devices and detecting possible transfer errors have increasing importance for metrological applications. We study the coupling of a superconducting Josephson-junction-based charge detector to an electron island defined by field-effect in silicon. The flexibility of our device allows one to tune the coupling using the detector as an additional gate electrode. We study the reliability of the electron sensor in different device configurations and the suitability of various operation modes for error detection in electron pumping experiments. As a result, we obtain a charge detection bandwidth of 5.87 kHz with unity signal to noise ratio at 300 mK bath temperature.

cond-mat.mes-hall↗

arXiv2019

Waiting time distributions in a two-level fluctuator coupled to a superconducting charge detector

We analyze charge fluctuations in a parasitic state strongly coupled to a superconducting Josephson-junction-based charge detector. The charge dynamics of the state resembles that of electron transport in a quantum dot with two charge states, and hence we refer to it as a two-level fluctuator. By constructing the distribution of waiting times from the measured detector signal and comparing it with a waiting time theory, we extract the electron in- and out-tunneling rates for the two-level fluctuator, which are severely asymmetric.

cond-mat.mes-hall↗

arXiv2019

Fast control of dissipation in a superconducting resonator

We report on fast tunability of an electromagnetic environment coupled to a superconducting coplanar waveguide resonator. Namely, we utilize a recently-developed quantum-circuit refrigerator (QCR) to experimentally demonstrate a dynamic tunability in the total damping rate of the resonator up to almost two orders of magnitude. Based on the theory it corresponds to a change in the internal damping rate by nearly four orders of magnitude. The control of the QCR is fully electrical, with the shortest implemented operation times in the range of 10 ns. This experiment constitutes a fast active reset of a superconducting quantum circuit. In the future, a similar scheme can potentially be used to initialize superconducting quantum bits.

quant-ph↗

arXiv2019

Calibration of cryogenic amplification chains using normal-metal--insulator--superconductor junctions

Various applications of quantum devices call for an accurate calibration of cryogenic amplification chains. To this end, we present a convenient calibration scheme and use it to accurately measure the total gain and noise temperature of an amplification chain by employing normal-metal--insulator--superconductor (NIS) junctions. Our method is based on the radiation emitted by inelastic electron tunneling across voltage-biased NIS junctions. We derive an analytical equation that relates the generated power to the applied bias voltage which is the only control parameter of the device. After the setup has been characterized using a standard voltage reflection measurement, the total gain and the noise temperature are extracted by fitting the analytical equation to the microwave power measured at the output of the amplification chain. The 1$σ$ uncertainty of the total gain of 51.84 dB appears to be of the order of 0.1 dB.

quant-ph↗

arXiv2019

Observation of a broadband Lamb shift in an engineered quantum system

The shift of energy levels owing to broadband electromagnetic vacuum fluctuations, the Lamb shift, has been pivotal in the development of quantum electrodynamics and in understanding atomic spectra. Currently, small energy shifts in engineered quantum systems are of paramount importance owing to the extreme precision requirements in applications such as quantum computing. However, without a tunable environment it is challenging to resolve the Lamb shift in its original broadband case. Consequently, the observations in other than atomic systems are limited to environments comprised of narrow-band modes. Here, we observe a broadband Lamb shift in high-quality superconducting resonators, a scenario also accessing static shifts inaccessible in Lamb's experiment. We measure a continuous change of several megahertz in the fundamental resonator frequency by externally tuning the coupling strength of the engineered broadband environment which is based on hybrid normal-metal--superconductor tunnel junctions. Our results may lead to improved control of dissipation in high-quality engineered quantum systems and open new possibilities for studying synthetic open quantum matter using this hybrid experimental platform.

cond-mat.mes-hall↗

arXiv2017

Flux-tunable heat sink for quantum electric circuits

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 $10^5$ down to a few thousand at 10 GHz in good quantitative agreement with our theoretical model.

cond-mat.mes-hall↗