arXiv subjects

Ville F. Maisi

Publications and source records attributed to Ville F. Maisi.

At least 19 recordsLinked to original sources

arXiv2026

Near-Unity Charge Readout in a Nonlinear Resonator without Matching

Dissipative sensors typically use linear resonators with impedance matching to achieve maximal signal and fast operation. The impedance matching, however, sets an upper limit to the bandwidth of the readout. In this paper, we present a nonlinear resonator performing the readout of a double quantum dot charge state via a charge-sensing quantum dot. We show that by driving the resonator in the nonlinear regime, we achieve a near-unity signal for a dissipative sensor. This despite not satisfying the sensor impedance matching requirements necessary for such large signals in the linear regime. Our experiments, supported by numerical calculations, demonstrate that the signal increase stems from the sensor dissipation shifting the onset of the nonlinear resonator response. By lifting the matching requirement, we open up an avenue to ultrafast charge detectors as the resonator input-output coupling - setting the detector bandwidth - does not have to match to the typically much slower sensor dissipation rate.

cond-mat.mes-hall↗

arXiv2026

Heat Conduction and Energy Relaxation in an InAs Nanowire Approaching the Clean One-Dimensional Limit

We investigate heat conduction and energy relaxation in an InAs semiconductor nanowire using a hybrid semiconductor-superconductor architecture. Local electronic temperatures are measured with an in-situ grown quantum dot thermometer, while controlled Joule heating is applied at different locations along the wire to probe temperature gradients at sub-kelvin temperatures. With a onedimensional heat transport model, we calculate an electron-phonon heat flow that scales as Q_{e-ph} \propto T^2.6, which is in close agreement with the T^3 dependence predicted for a clean one-dimensional electron gas coupled to a phonon bath. We further estimate a characteristic length l_{eq} = 370 nm, beyond this length scale, phonon-mediated heat transport dominates over heat conduction in our nanowire. Our results provide a quantitative measure of energy relaxation mechanisms in a onedimensional semiconductor and provide a framework for studying heat flow in low-dimensional nanostructures.

cond-mat.mes-hall↗

arXiv2025

High-efficiency microwave photodetection by cavity coupled double dots with single cavity-photon sensitivity

We present a superconducting cavity-coupled double quantum dot (DQD) photodiode that achieves a maximum photon-to-electron conversion efficiency of 25% in the microwave domain. With a higher-quality-factor cavity and improved device design to prevent photon leakages through unwanted pathways, our device measures microwave signals down to 100 aW power level and achieves sensitivity to probe microwave signals with one photon at a time in the cavity. We analyze the photodiode operation using Jaynes-Cummings input-output theory, identifying the key improvements of stronger cavity-DQD coupling needed to achieve near-unity photodetection efficiency. The results presented in this work represent a crucial advancement toward near unity microwave photodetection efficiency with single cavity-photon sensitivity for studies of photon statistics in the microwave range and applications related to quantum information processing.

cond-mat.mes-hall↗

arXiv2025

High-Efficiency Tunable Microwave Photon Detector Based on a Semiconductor Double Quantum Dot Coupled to a Superconducting High-Impedance Cavity

High-efficiency single-photon detection in the microwave domain is a key enabling technology for quantum sensing, communication, and information processing. However, the extremely low energy of microwave photons (~μeV) presents a fundamental challenge, preventing direct photon-to-charge conversion as achieved in optical systems using semiconductors. Semiconductor quantum dot (QD) charge qubits offer a compelling solution due to their highly tunable energy levels in the microwave regime, enabling coherent coupling with single photons. In this work, we demonstrate microwave photon detection with an efficiency approaching 70% in the single-photon regime. We use a hybrid system comprising a double quantum dot (DQD) charge qubit electrostatically defined in a GaAs/AlGaAs heterostructure, coupled to a high-impedance Josephson junction (JJ) array cavity. We systematically optimize the hybrid device architecture to maximize the conversion efficiency, leveraging the strong charge-photon coupling and the tunable DQD tunnel coupling rates. Incoming cavity photons coherently excite the DQD qubit, which in turn generates a measurable electrical current, realizing deterministic photon-to-charge conversion. Moreover, by exploiting the independent tunability of both the DQD transition energy and the cavity resonance frequency, we characterize the system efficiency over a range of 3-5.2 GHz. Our results establish semiconductor-based cavity-QED architectures as a scalable and versatile platform for efficient microwave photon detection, opening new avenues for quantum microwave optics and hybrid quantum information technologies.

quant-ph↗

arXiv2024

Coherence of an Electronic Two-Level System under Continuous Charge Sensing by a Quantum Dot Detector

We investigate experimentally the quantum coherence of an electronic two-level system in a double quantum dot under continuous charge detection. The charge-state of the two-level system is monitored by a capacitively coupled single quantum dot detector that imposes a back-action effect to the system. The measured back-action is well described by an additional decoherence rate, approximately linearly proportional to the detector electron tunneling rate. We provide a model for the decoherence rate arising due to level detuning fluctuations induced by detector charge fluctuations. The theory predicts a factor of two lower decoherence rate than observed in the experiment, suggesting the need for a more elaborate theory accounting for additional sources of decoherence.

cond-mat.mes-hall↗

arXiv2024

A coherence sweet spot with enhanced dipolar coupling

Qubits require a compromise between operation speed and coherence. Here, we demonstrate a compromise-free singlet-triplet (ST) qubit, where the qubit couples maximally to the driving field while simultaneously coupling minimally to the dominant noise sources. The qubit is implemented in a crystal-phase defined double-quantum dot in an InAs nanowire. Using a superconducting resonator, we measure the spin-orbit interaction (SOI) gap, the spin-photon coupling strength and the qubit decoherence rate as a function of the in-plane magnetic-field orientation. We demonstrate a spin qubit sweet spot maximizing the dipolar coupling and simultaneously minimizing the decoherence. Our theoretical description postulates phonons as the most likely dominant noise source. The compromise-free sweet spot originates from the SOI suggesting that it is not restricted to this material platform, but might find applications in any material with SOI. These findings pave the way for enhanced engineering of these nanomaterials for next-generation qubit technologies.

cond-mat.mes-hall↗

arXiv2024

Microwave power harvesting using resonator-coupled double quantum dot photodiode

We demonstrate a microwave power-to-electrical energy conversion in a resonator-coupled double quantum dot. The system, operated as a photodiode, converts individual microwave photons to electrons tunneling through the double dot, resulting in an electrical current flowing against the applied voltage bias at input powers down to 1 femto-watt. The device attains a maximum power harvesting efficiency of 2%, with the photon-to-electron conversion efficiency reaching 12% in the single photon absorption regime. We find that the power conversion depends on thermal effects showing that thermodynamics plays a crucial role in the single photon energy conversion.

cond-mat.mes-hall↗

arXiv2024

Continuous microwave photon counting by semiconductor-superconductor hybrids

The growing interest in quantum information has enabled the manipulation and readout of microwave photon states with high fidelities. The presently available microwave photon counters, based on superconducting circuits, are limited to non-continuous pulsed mode operation, requiring additional steps for qubit state preparation before an actual measurement. Here, we present a continuous microwave photon counter based on superconducting cavity-coupled semiconductor quantum dots. The device utilizes photon-assisted tunneling in a double quantum dot with tunneling events being probed by a third dot. Our device detects both single and multiple-photon absorption events independently, thanks to the energy tunability of a two-level double-dot absorber. We show that the photon-assisted tunnel rates serve as the measure of the cavity photon state in line with the P(E) theory - a theoretical framework delineating the mediation of the cavity photon field via a two-level environment. We further describe the single photon detection using the Jaynes-Cummings input-output theory and show that it agrees with the P(E) theory predictions.

cond-mat.mes-hall↗

arXiv2023

High Impedance Josephson Junction Resonators in the Transmission Line Geometry

In this article we present an experimental study of microwave resonators made out of Josephson junctions. The junctions are embedded in a transmission line geometry so that they increase the inductance per length for the line. By comparing two devices with different input/output coupling strengths, we show that the coupling capacitors, however, add a significant amount to the total capacitance of the resonator. This makes the resonators with high coupling capacitance to act rather as lumped element resonators with inductance from the junctions and capacitance from the end sections. Based on a circuit analysis, we show that the input and output couplings of the resonator are limited to a maximum value of $ω_r Z_0 /4 Z_r$ where $ω_r$ is the resonance frequency and $Z_0$ and $Z_r$ are the characteristic impedances of the input/output lines and the resonator respectively.

cond-mat.mes-hall↗

arXiv2023

Strong coupling between a microwave photon and a singlet-triplet qubit

Tremendous progress in few-qubit quantum processing has been achieved lately using superconducting resonators coupled to gate voltage defined quantum dots. While the strong coupling regime has been demonstrated recently for odd charge parity flopping mode spin qubits, first attempts towards coupling a resonator to even charge parity singlet-triplet spin qubits have resulted only in weak spin-photon coupling strengths. Here, we integrate a zincblende InAs nanowire double quantum dot with strong spin-orbit interaction in a magnetic-field resilient, high-quality resonator. In contrast to conventional strategies, the quantum confinement is achieved using deterministically grown wurtzite tunnel barriers without resorting to electrical gating. Our experiments on even charge parity states and at large magnetic fields, allow to identify the relevant spin states and to measure the spin decoherence rates and spin-photon coupling strengths. Most importantly, we find an anti-crossing between the resonator mode in the single photon limit and a singlet-triplet qubit with an electron spin-photon coupling strength of $g/2π=139\pm4$ MHz. Combined with the resonator decay rate $κ/2π=19.8\pm0.2$ MHz and the qubit dephasing rate $γ/2π=116\pm7$ MHz, our system achieves the strong coupling regime in which the coherent coupling exceeds qubit and resonator linewidth. These results pave the way towards large-scale quantum system based on singlet-triplet qubits.

cond-mat.mes-hall↗

arXiv2023

Dephasing in a crystal-phase defined double quantum dot charge qubit strongly coupled to a high-impedance resonator

Dephasing of a charge qubit is usually credited to charge noise in the environment. Here we show that charge noise may not be the limiting factor for the qubit coherence. To this end, we study coherence properties of a crystal-phase defined semiconductor nanowire double quantum dot (DQD) charge qubit strongly coupled to a high-impedance resonator using radio-frequency (RF) reflectometry. Response of this hybrid system is measured both at a charge noise sensitive operation point (with finite DQD detuning) and at an insensitive point (so-called sweet spot with zero detuning). A theoretical model based on Jaynes-Cummings Hamiltonian matches the experimental results well and yields only a 10 % difference in dephasing rates between the two cases, despite that the sensitivity to detuning charge noise differs by a factor of 5. Therefore the charge noise is not the limiting factor for the coherence in this type of semiconducting nanowire qubits.

cond-mat.mes-hall↗

arXiv2023

Quantum Dot Source-Drain Transport Response at Microwave Frequencies

Quantum dots are frequently used as charge sensitive devices in low temperature experiments to probe electric charge in mesoscopic conductors where the current running through the quantum dot is modulated by the nearby charge environment. Recent experiments have been operating these detectors using reflectometry measurements up to GHz frequencies rather than probing the low frequency current through the dot. In this work, we use an on-chip coplanar waveguide resonator to measure the source-drain transport response of two quantum dots at a frequency of 6 GHz, further increasing the bandwidth limit for charge detection. Similar to the low frequency domain, the response is here predominantly dissipative. For large tunnel coupling, the response is still governed by the low frequency conductance, in line with Landauer-Büttiker theory. For smaller couplings, our devices showcase two regimes where the high frequency response deviates from the low frequency limit and Landauer-Büttiker theory: When the photon energy exceeds the quantum dot resonance linewidth, degeneracy dependent plateaus emerge. These are reproduced by sequential tunneling calculations. In the other case with large asymmetry in the tunnel couplings, the high frequency response is two orders of magnitude larger than the low frequency conductance G, favoring the high frequency readout.

cond-mat.mes-hall↗

arXiv2023

Minimally dissipative information erasure in a quantum dot via thermodynamic length

In this work we explore the use of thermodynamic length to improve the performance of experimental protocols. In particular, we implement Landauer erasure on a driven electron level in a semiconductor quantum dot, and compare the standard protocol in which the energy is increased linearly in time with the one coming from geometric optimisation. The latter is obtained by choosing a suitable metric structure, whose geodesics correspond to optimal finite-time thermodynamic protocols in the slow driving regime. We show experimentally that geodesic drivings minimise dissipation for slow protocols, with a bigger improvement as one approaches perfect erasure. Moreover, the geometric approach also leads to smaller dissipation even when the time of the protocol becomes comparable with the equilibration timescale of the system, i.e., away from the slow driving regime. Our results also illustrate, in a single-electron device, a fundamental principle of thermodynamic geometry: optimal finite-time thermodynamic protocols are those with constant dissipation rate along the process.

cond-mat.mes-hall↗

arXiv2022

Energetics of microwaves probed by double quantum dot absorption

We explore the energetics of microwaves interacting with a double quantum dot photodiode and show wave-particle aspects in photon-assisted tunneling. The experiments show that the single photon energy sets the relevant absorption energy in a weak-drive limit, which contrasts the strong drive limit where the wave amplitude determines the relevant-energy scale and opens up microwave induced bias triangles. The threshold condition between these two regimes is set by the fine-structure constant of the system. The energetics are determined here with the detuning conditions of the double dot system and stopping-potential measurements that constitute a microwave version of the photoelectric effect.

cond-mat.mes-hall↗

arXiv2022

Local and non-local two-electron tunneling processes in a Cooper pair splitter

We measure the tunneling rates and coupling coefficients for local Andreev, non-local Andreev and elastic cotunneling processes. The non-local Andreev process, giving rise to Cooper pair splitting, exhibits the same coupling coefficient as the elastic co-tunneling whereas the local Andreev process is more than two orders of magnitude stronger than the corresponding non-local one. Theory estimates describe the findings and explain the large difference in the non-local and local coupling arising from competition between electron diffusion in the superconductor and tunnel junction transparency.

cond-mat.mes-hall↗

arXiv2022

Efficient and Continuous Microwave Photodetection in Hybrid Cavity-Semiconductor Nanowire Double Quantum Dot Diodes

Single photon detectors are key for time-correlated photon counting applications [1] and enable a host of emerging optical quantum information technologies [2]. So far, the leading approach for continuous and efficient single-photon detection in the optical domain has been based on semiconductor photodiodes [3]. However, there is a paucity of efficient and continuous single-photon detectors in the microwave regime, because photon energies are four to five orders of magnitude lower therein and conventional photodiodes do not have that sensitivity. Here we tackle this gap and demonstrate how itinerant microwave photons can be efficiently and continuously converted to electrical current in a high-quality, semiconducting nanowire double quantum dot that is resonantly coupled to a cavity. In particular, in our detection scheme, an absorbed photon gives rise to a single electron tunneling event through the double dot, with a conversion efficiency reaching 6 %. Our results pave the way for photodiodes with single-shot microwave photon detection, at the theoretically predicted unit efficiency [4].

cond-mat.mes-hall↗

arXiv2021

Real-time observation of Cooper pair splitting showing strong non-local correlations

Controlled generation and detection of quantum entanglement between spatially separated particles constitute an essential prerequisite both for testing the foundations of quantum mechanics and for realizing future quantum technologies. Splitting of Cooper pairs from a superconductor provides entangled electrons at separate locations. However, experimentally accessing the individual split Cooper pairs constitutes a major unresolved issue as they mix together with electrons from competing processes. Here, we overcome this challenge with the first real-time observation of the splitting of individual Cooper pairs, enabling direct access to the time-resolved statistics of Cooper pair splitting. We determine the correlation statistics arising from two-electron processes and find a pronounced peak that is two orders of magnitude larger than the background. Our experiment thereby allows to unambiguously pinpoint and select split Cooper pairs with 99 % fidelity. These results open up an avenue for performing experiments that tap into the spin-entanglement of split Cooper pairs.

cond-mat.mes-hall↗

arXiv2021

Experimental verification of the work fluctuation-dissipation relation for information-to-work conversion

We study experimentally work fluctuations in a Szilard engine that extracts work from information encoded as the occupancy of an electron level in a semiconductor quantum dot. We show that as the average work extracted per bit of information increases towards the Landauer limit $k_BT \ln 2$, the work fluctuations decrease in accordance with the work fluctuation-dissipation relation. We compare the results to a protocol without measurement and feedback and show that when no information is used, the work output and fluctuations vanish simultaneously contrasting the information-to-energy conversion case where increasing amount of work is produced with decreasing fluctuations. Our work highlights the importance of fluctuations in the design of information-to-work conversion processes.

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