Challenges
Datasets
Workspaces
Papers
Discussions
Leaderboard
Log inSign up
Challenges
Datasets
Workspaces
Papers
Discussions
Leaderboard
Blog
Job Board
Q3AS

© 2026 Aqora Quantum S.A.S.

TermsPrivacyLegal Notice

Investigating Quasiparticle Poisoning in Floating Hybrid Double Dot Devices Using Gate-Based Sensing

Nejc Blaznik

Published Jan 1, 2020• 0 citations
OpenAlex

Abstract

One of the essential limitations for a physical realisation of topological-qubit based quantum computing is the problem of uncontrolled quasiparticle poisoning of the superconducting charge island. These quasiparticles have been previously reported as a known limiting factor in most of the superconducting architectures. To this end, we consider the importance of equilibrium quasiparticle poisoning in hybrid semiconducting-superconducting systems believed to be able to host Majoranas. We employed gate-based dispersive sensing by investigating a reflected radiofrequency (RF) signal from a resonator, which is capacitively coupled to one of the gate electrodes of the hybrid double dot realised in an InAs nanowire. This way, the quantum capacitance of the system can be probed, which in turn reveals charge tunnelling processes, and can be used as an indicator of single-electron tunnelling events. By operating the device in a so-called floating regime, where a double dot system is entirely decoupled from the leads, external non-equilibrium quasiparticle poisoning events can be exponentially suppressed. By appropriately tuning the chemical potentials on the quantum dot and the superconducting island, we attempt to scrutinise the dynamics of the quasiparticles innate to the superconductor. We investigated the dependence of quasiparticle tunnelling rates on the temperature of the system, as well as the applied RF power, as both are predicted to increase the average number of quasiparticles on the island. In both cases, we could find no observational proof of quasiparticle tunnelling events through the use of our measurement technique. We report an observation of a two-level resonator response, which we explain using a two-level fluctuator. Analysing telegraph measurements, we demonstrate the viability of the analysis tool, which allows us to determine the average occupation times of each state. In principle, for processes occurring at rates slower than the measurement frequency, this technique can be used to convert a\nrelatively faint difference between the “poisoned and unpoisoned state”, to the signal of the gate being on coulomb resonance versus on Coulomb blockade, which is a much clearer signal to distinguish. Both, the technique, as well as the expected rates of the physical processes within the island, are evaluated in the context of the experiment.

Related papers

Dispersive Gate Sensing of Hybrid Quantum Dot Systems

Christian G. Prosko

Spin and topological-qubit based quantum computers require an easily scalable and highly sensitive method for readout and manipulation, for which Dispersive Gate Sensing (DGS) is a promising candidate [1, 2]. DGS enables sensing of single electron tunneling events in a mesoscopic system by measuring a reflected Radio Frequency (RF) signal from a resonator capacitively coupled to one of the system’s gate electrodes. From the resonator’s perspective, the system is modeled as an effective ‘parametric capacitance’ [3]. Motivated by its viability for qubit readout and control, we measure transport characteristics of a semiconducting-superconducting hybrid charge island system using this method. Doing so, we observe a spin degeneracy modulation of interdot tunnel couplings resulting from hybridization of a dot orbital with a subgap state of the superconductor, measured entirely within Coulomb blockade. Without DC measurement, we also track a subgap state’s energy via voltage intervals between island charge states as a function of field. Subsequently, we attempt to correlate changes in the resonator’s internal dissipation with coherence of tunneling into the superconducting island. In particular, we collapse a superconducting island’s lowest energy state to the Fermi level by applying a magnetic field. Contrary to expectations, internal dissipation in the resonator did not change dramatically with field, in fact decreasing at charge degeneracy points at all field strengths. We corroborate measurements with existing theory, augmented by simple analytical and numerical models demonstrating that coherence factors of superconducting quasiparticle states and the degeneracy of dot orbitals modulate parametric capacitance. A master equation model of finite temperature interdot tunneling is solved, agreeing with experimental evidence that Sisyphus dissipation is negligible when a dot orbital is hybridized with multiple independent quasiparticle states. To be employed in quantum computers, a full understanding of all phenomena contributing to a DGS signal in these hybrid systems is critical. Hence, these results mark a step towards unambiguous readout of Majorana parity in topological qubits [4].

•Jan 1, 2019•0 citations

Superconducting islands and gate-based readout in semiconductor nanowires

Jasper van Veen

Quantum computers can solve some problems exponentially faster than classical computers. Unfortunately, the computational power of quantum computers is currently limited by the number of working qubits. It is difficult to scale up these systems, because qubits are easily affected by noise in their environment. This noise leads to decoherence: loss of the qubit’s encoded information. A possible solution to diminish decoherence is using Majorana box qubits, as these qubits are predicted to be insensitive to local noise. However, this promising type of qubit does not exist yet. With the research described in this thesis, we aim to contribute to the development of Majorana box qubits (MBQs). In these qubits, Majorana zero modes, the basic elements of MBQs, are contained within a superconducting island to suppress Majorana parity fluctuations caused by quasiparticle poisoning. To enable parity readout of the MBQ, these modes are coupled to quantum dots within a nanowire network. To help realize MBQs, we need a better understanding of quasiparticles in superconducting islands, parity-readout techniques, and ways to fabricate nanowire networks. These three aspects are the focus of the experiments presented in this thesis. To study superconducting islands and readout techniques, we used InAs semiconductor nanowires with an epitaxially grown Al shell. Majorana signatures have already been observed in such nanowires. We addressed quasiparticle dynamics in superconducting islands by measuring the gate-charge modulation of the switching current. We found a consistent 2e-periodic modulation at zero magnetic field, and an exponential decrease of parity lifetime with increasing magnetic field. We explored MBQ readout, using a quantum dot level as a proxy for a Majorana zero mode, and measured its charge hybridization with another dot using gate-based readout. We showed that we can rapidly discriminate between two settings with different tunnel couplings, demonstrating the potential of gate-based readout to measure MBQs. And, using gate-based readout, we could study charge-transfer processes occurring in hybrid structures of superconducting islands coupled to quantum dots. Finally, to find a good material platform for nanowire networks, we characterized two two-dimensional systems. We realized quantum point contacts in InSb, which we used to measure the $g$-factor anisotropy, and effective electron mass in this system. And, we studied the spin-orbit interaction in InAs/GaSb by extracting the difference in density between electrons with different spin orientations. This thesis finishes with a proposal for a series experiments to realize MBQs. These experiments make use of superconducting islands and the reflectometry setup we developed for gate-based readout.

•May 15, 2019•0 citations

Observation of Cooper pair tunnelling in a galvanically isolated superconducting double dot via quantum capacitance

A. A. Esmail, Andrew J. Ferguson, N. J. Lambert

We increase the isolation of a superconducting double dot from its environment by galvanically isolating it from any electrodes. We probe it using high frequency reflectometry techniques, find 2e-periodic behaviour, and characterise the energy structure of its charge states. By modelling the response of the device, we determine the quasiparticle poisoning rate to be significantly worse than that of a unisolated double dot, and conclude that quasiparticle exchange between the dot and the leads is an important relaxation mechanism.

•Sep 22, 2017•0 citations

Cooper pair tunnelling and quasiparticle poisoning in a galvanically isolated superconducting double dot

A. A. Esmail, Andrew J. Ferguson, N. J. Lambert

We increase the isolation of a superconducting double dot from its environment by galvanically isolating it from any electrodes. We probe it using high frequency reflectometry techniques, find 2e-periodic behaviour, and characterise the energy structure of its charge states. By modelling the response of the device, we determine the time averaged probability that the device is poisoned by quasiparticles, and by comparing this with previous work, we conclude that quasiparticle exchange between the dots and the leads is an important relaxation mechanism.

arXiv:1709.07815•Applied Physics Letters•Dec 18, 2017•4 citations

Using Quasiparticle Poisoning To Detect Photons

P. M. Echternach, Peter K. Day

According to a proposal, a phenomenon associated with excitation of quasiparticles in certain superconducting quantum devices would be exploited as a means of detecting photons with exquisite sensitivity. The phenomenon could also be exploited to perform medium-resolution spectroscopy. The proposal was inspired by the observation that Coulomb blockade devices upon which some quantum logic gates are based are extremely sensitive to quasiparticles excited above the superconducting gaps in their leads. The presence of quasiparticles in the leads can be easily detected via the charge states. If quasiparticles could be generated in the leads by absorption of photons, then the devices could be used as very sensitive detectors of electromagnetic radiation over the spectral range from x-rays to submillimeter waves. The devices in question are single-Cooper-pair boxes (SCBs), which are mesoscopic superconducting devices developed for quantum computing. An SCB consists of a small superconducting island connected to a reservoir via a small tunnel junction and connected to a voltage source through a gate capacitor. An SCB is an artificial two-level quantum system, the Hamiltonian of which can be controlled by the gate voltage. One measures the expected value of the charge of the eigenvectors of this quantum system by use of a radio-frequency single-electron transistor. A plot of this expected value of charge as a function of gate voltage resembles a staircase that, in the ideal case, consists of steps of height 2 e (where e is the charge of one electron). Experiments have shown that depending on the parameters of the device, quasiparticles in the form of "broken" Cooper pairs present in the reservoir can tunnel to the island, giving rise to steps of 1 e. This effect is sometimes called "poisoning." Simulations have shown that an extremely small average number of quasiparticles can generate a 1-e periodic signal. In a device according to the proposal, this poisoning would be turned to advantage. Depending on the wavelength, an antenna or other component would be used to couple radiation into the reservoir, wherein the absorption of photons would break Cooper pairs, thereby creating quasiparticles that, in turn, would tunnel to the island, creating a 1-e signal. On the basis of conservative estimates of device parameters derived from experimental data and computational simulations that fit the data, it has been estimated that the noise equivalent power of a device according to the proposal could be as low as 6 10(exp -22) W/Hz(exp 1/2). It has also been estimated that the spectroscopic resolution (photon energy divided by increment of photon energy) of such a device in visible light would exceed 100.

•Mar 1, 2006•0 citations

Thin-film aluminium for superconducting qubits

Andrew J. Ferguson, Nadia Court, Fay E. Hudson +1 more

We study single-Cooper-pair-transistors in which the island is made from an ultra-thin (10nm) aluminum film. The value of the superconducting gap (2Delta) changes dramatically with film thickness therefore allowing different superconducting gaps for the islands and leads simply by using different film thicknesses. Devices engineered in this way can be made less susceptible to having a single quasiparticle trapped on the island (often known as the quasiparticle poisoning problem). This is an advantage for charge-based superconducting qubits where quasiparticle poisoning is a source of decoherence. We perform radio-frequency measurements and observe 2e-periodic supercurrent peaks as a function of gate charge. With the device biased on a supercurrent oscillation, a fast random-telegraph signal due to individual quasiparticle poisoning events is observed. By analyzing the statistics of the poisoning and un-poisoning events we determine the energetics and thermal activation of these processes

•Jan 1, 2006•1 citation
One of the essential limitations for a physical realisation of topological-qubit based quantum computing is the problem of uncontrolled quasiparticle poisoning of the superconducting charge island. These quasiparticles have been previously reported as a known limiting factor in most of the superconducting architectures. To this end, we consider the importance of equilibrium quasiparticle poisoning in hybrid semiconducting-superconducting systems believed to be able to host Majoranas. We employed gate-based dispersive sensing by investigating a reflected radiofrequency (RF) signal from a resonator, which is capacitively coupled to one of the gate electrodes of the hybrid double dot realised in an InAs nanowire. This way, the quantum capacitance of the system can be probed, which in turn reveals charge tunnelling processes, and can be used as an indicator of single-electron tunnelling events. By operating the device in a so-called floating regime, where a double dot system is entirely decoupled from the leads, external non-equilibrium quasiparticle poisoning events can be exponentially suppressed. By appropriately tuning the chemical potentials on the quantum dot and the superconducting island, we attempt to scrutinise the dynamics of the quasiparticles innate to the superconductor. We investigated the dependence of quasiparticle tunnelling rates on the temperature of the system, as well as the applied RF power, as both are predicted to increase the average number of quasiparticles on the island. In both cases, we could find no observational proof of quasiparticle tunnelling events through the use of our measurement technique. We report an observation of a two-level resonator response, which we explain using a two-level fluctuator. Analysing telegraph measurements, we demonstrate the viability of the analysis tool, which allows us to determine the average occupation times of each state. In principle, for processes occurring at rates slower than the measurement frequency, this technique can be used to convert a\nrelatively faint difference between the “poisoned and unpoisoned state”, to the signal of the gate being on coulomb resonance versus on Coulomb blockade, which is a much clearer signal to distinguish. Both, the technique, as well as the expected rates of the physical processes within the island, are evaluated in the context of the experiment.
Spin and topological-qubit based quantum computers require an easily scalable and highly sensitive method for readout and manipulation, for which Dispersive Gate Sensing (DGS) is a promising candidate [1, 2]. DGS enables sensing of single electron tunneling events in a mesoscopic system by measuring a reflected Radio Frequency (RF) signal from a resonator capacitively coupled to one of the system’s gate electrodes. From the resonator’s perspective, the system is modeled as an effective ‘parametric capacitance’ [3]. Motivated by its viability for qubit readout and control, we measure transport characteristics of a semiconducting-superconducting hybrid charge island system using this method. Doing so, we observe a spin degeneracy modulation of interdot tunnel couplings resulting from hybridization of a dot orbital with a subgap state of the superconductor, measured entirely within Coulomb blockade. Without DC measurement, we also track a subgap state’s energy via voltage intervals between island charge states as a function of field. Subsequently, we attempt to correlate changes in the resonator’s internal dissipation with coherence of tunneling into the superconducting island. In particular, we collapse a superconducting island’s lowest energy state to the Fermi level by applying a magnetic field. Contrary to expectations, internal dissipation in the resonator did not change dramatically with field, in fact decreasing at charge degeneracy points at all field strengths. We corroborate measurements with existing theory, augmented by simple analytical and numerical models demonstrating that coherence factors of superconducting quasiparticle states and the degeneracy of dot orbitals modulate parametric capacitance. A master equation model of finite temperature interdot tunneling is solved, agreeing with experimental evidence that Sisyphus dissipation is negligible when a dot orbital is hybridized with multiple independent quasiparticle states. To be employed in quantum computers, a full understanding of all phenomena contributing to a DGS signal in these hybrid systems is critical. Hence, these results mark a step towards unambiguous readout of Majorana parity in topological qubits [4].
Quantum computers can solve some problems exponentially faster than classical computers. Unfortunately, the computational power of quantum computers is currently limited by the number of working qubits. It is difficult to scale up these systems, because qubits are easily affected by noise in their environment. This noise leads to decoherence: loss of the qubit’s encoded information. A possible solution to diminish decoherence is using Majorana box qubits, as these qubits are predicted to be insensitive to local noise. However, this promising type of qubit does not exist yet. With the research described in this thesis, we aim to contribute to the development of Majorana box qubits (MBQs). In these qubits, Majorana zero modes, the basic elements of MBQs, are contained within a superconducting island to suppress Majorana parity fluctuations caused by quasiparticle poisoning. To enable parity readout of the MBQ, these modes are coupled to quantum dots within a nanowire network. To help realize MBQs, we need a better understanding of quasiparticles in superconducting islands, parity-readout techniques, and ways to fabricate nanowire networks. These three aspects are the focus of the experiments presented in this thesis. To study superconducting islands and readout techniques, we used InAs semiconductor nanowires with an epitaxially grown Al shell. Majorana signatures have already been observed in such nanowires. We addressed quasiparticle dynamics in superconducting islands by measuring the gate-charge modulation of the switching current. We found a consistent 2e-periodic modulation at zero magnetic field, and an exponential decrease of parity lifetime with increasing magnetic field. We explored MBQ readout, using a quantum dot level as a proxy for a Majorana zero mode, and measured its charge hybridization with another dot using gate-based readout. We showed that we can rapidly discriminate between two settings with different tunnel couplings, demonstrating the potential of gate-based readout to measure MBQs. And, using gate-based readout, we could study charge-transfer processes occurring in hybrid structures of superconducting islands coupled to quantum dots. Finally, to find a good material platform for nanowire networks, we characterized two two-dimensional systems. We realized quantum point contacts in InSb, which we used to measure the ggg-factor anisotropy, and effective electron mass in this system. And, we studied the spin-orbit interaction in InAs/GaSb by extracting the difference in density between electrons with different spin orientations. This thesis finishes with a proposal for a series experiments to realize MBQs. These experiments make use of superconducting islands and the reflectometry setup we developed for gate-based readout.
We increase the isolation of a superconducting double dot from its environment by galvanically isolating it from any electrodes. We probe it using high frequency reflectometry techniques, find 2e-periodic behaviour, and characterise the energy structure of its charge states. By modelling the response of the device, we determine the quasiparticle poisoning rate to be significantly worse than that of a unisolated double dot, and conclude that quasiparticle exchange between the dot and the leads is an important relaxation mechanism.
We increase the isolation of a superconducting double dot from its environment by galvanically isolating it from any electrodes. We probe it using high frequency reflectometry techniques, find 2e-periodic behaviour, and characterise the energy structure of its charge states. By modelling the response of the device, we determine the time averaged probability that the device is poisoned by quasiparticles, and by comparing this with previous work, we conclude that quasiparticle exchange between the dots and the leads is an important relaxation mechanism.
According to a proposal, a phenomenon associated with excitation of quasiparticles in certain superconducting quantum devices would be exploited as a means of detecting photons with exquisite sensitivity. The phenomenon could also be exploited to perform medium-resolution spectroscopy. The proposal was inspired by the observation that Coulomb blockade devices upon which some quantum logic gates are based are extremely sensitive to quasiparticles excited above the superconducting gaps in their leads. The presence of quasiparticles in the leads can be easily detected via the charge states. If quasiparticles could be generated in the leads by absorption of photons, then the devices could be used as very sensitive detectors of electromagnetic radiation over the spectral range from x-rays to submillimeter waves. The devices in question are single-Cooper-pair boxes (SCBs), which are mesoscopic superconducting devices developed for quantum computing. An SCB consists of a small superconducting island connected to a reservoir via a small tunnel junction and connected to a voltage source through a gate capacitor. An SCB is an artificial two-level quantum system, the Hamiltonian of which can be controlled by the gate voltage. One measures the expected value of the charge of the eigenvectors of this quantum system by use of a radio-frequency single-electron transistor. A plot of this expected value of charge as a function of gate voltage resembles a staircase that, in the ideal case, consists of steps of height 2 e (where e is the charge of one electron). Experiments have shown that depending on the parameters of the device, quasiparticles in the form of "broken" Cooper pairs present in the reservoir can tunnel to the island, giving rise to steps of 1 e. This effect is sometimes called "poisoning." Simulations have shown that an extremely small average number of quasiparticles can generate a 1-e periodic signal. In a device according to the proposal, this poisoning would be turned to advantage. Depending on the wavelength, an antenna or other component would be used to couple radiation into the reservoir, wherein the absorption of photons would break Cooper pairs, thereby creating quasiparticles that, in turn, would tunnel to the island, creating a 1-e signal. On the basis of conservative estimates of device parameters derived from experimental data and computational simulations that fit the data, it has been estimated that the noise equivalent power of a device according to the proposal could be as low as 6 10(exp -22) W/Hz(exp 1/2). It has also been estimated that the spectroscopic resolution (photon energy divided by increment of photon energy) of such a device in visible light would exceed 100.
We study single-Cooper-pair-transistors in which the island is made from an ultra-thin (10nm) aluminum film. The value of the superconducting gap (2Delta) changes dramatically with film thickness therefore allowing different superconducting gaps for the islands and leads simply by using different film thicknesses. Devices engineered in this way can be made less susceptible to having a single quasiparticle trapped on the island (often known as the quasiparticle poisoning problem). This is an advantage for charge-based superconducting qubits where quasiparticle poisoning is a source of decoherence. We perform radio-frequency measurements and observe 2e-periodic supercurrent peaks as a function of gate charge. With the device biased on a supercurrent oscillation, a fast random-telegraph signal due to individual quasiparticle poisoning events is observed. By analyzing the statistics of the poisoning and un-poisoning events we determine the energetics and thermal activation of these processes