Phase dynamics has been measured in a driven mesoscopic Josephson oscillator where the resonance ... more Phase dynamics has been measured in a driven mesoscopic Josephson oscillator where the resonance is tuned either by magnetic flux or by gate charge modulation of the Josephson inductance. Phenomena are analyzed in terms of a "phase particle picture", and by numerical circuit simulations. An analogy to switching of a DC-biased junction into voltage state is discussed. Operation principle of the recently demonstrated Inductive Single-Electron Transistor (L-SET) based on the driven oscillator is reviewed. The obtained charge sensitivity implies that a performance comparable to the best rf-SETs has already been reached with the novel device.
Single electron transistors (SET) are fabricated from multiwalled carbon nanotubes (MWNT) by mani... more Single electron transistors (SET) are fabricated from multiwalled carbon nanotubes (MWNT) by manipulation with an atomic force microscope. The devices consist of either a single MWNT with Au contacts at the ends or of two crossing tubes. In the latter device, the lower nanotube acted as the central island of a single electron transistor while the upper one functioned as
We discuss how a single Cooper-pair transistor may be used to detect the superconducting phase di... more We discuss how a single Cooper-pair transistor may be used to detect the superconducting phase difference by using the phase dependence of the input capacitance from gate to ground. The proposed device has a low power dissipation because its operation is in principle free from quasiparticle generation. According to the sensitivity estimates, the device may be used for efficient qubit readout in a galvanically isolated and symmetrized circuit.
We demonstrate a sensitive method of charge detection based on radio-frequency readout of the Jos... more We demonstrate a sensitive method of charge detection based on radio-frequency readout of the Josephson inductance of a superconducting single-electron transistor. Charge sensitivity 1.4 ×10 4e/ √ Hz, limited by preamplifier, is achieved in an operation mode which takes advantage of the nonlinearity of the Josephson potential. Owing to reactive readout, our setup has more than two orders of magnitude lower dissipation than the existing method of radio-frequency elec- trometry. With an optimized sample, we expect uncoupled energy sensitivity below ~ in the same experimental scheme.
Using a classical equation of motion, dynamics of the phase is analyzed in the Inductive Single-E... more Using a classical equation of motion, dynamics of the phase is analyzed in the Inductive Single-Electron Transistor (L-SET) which is a promising new system suitable for quantum measurement with ultimate sensitivity and low back-action. In a regime of nonlinear dynamics, a shift of the oscillator resonant frequency is discovered which has a direct analogy to the switching of a dc-biased Josephson junction into voltage state. Results are reviewed for the predicted charge sensitivity, and it is shown that a performance challenging the best rf-SETs is foreseeable with the new device.
Low-frequency susceptibility of the split Cooper-pair box (SCPB) is investigated for use in sensi... more Low-frequency susceptibility of the split Cooper-pair box (SCPB) is investigated for use in sensitive measurements of external phase or charge. Depending on the coupling scheme, the box appears as either inductive or capacitive reactance which depends on external phase and charge. While coupling to the source-drain phase, we review how the SCPB looks like a tunable inductance, which property we used to build a novel radio-frequency electrometer. In the dual mode of operation, that is, while observed at the gate input, the SCPB looks like a capacitance. We concentrate on discussing the latter scheme, and we show how to do studies of fast phase fluctuations at a sensitivity of 1 mrad/ √ Hz by measuring the input capacitance of the box.
ABSTRACT We investigate the possibility of using multiwalled carbon nanotubes for constructing lo... more ABSTRACT We investigate the possibility of using multiwalled carbon nanotubes for constructing low-noise single-electron transistors (SETs). We use free-standing structures where the carbon nanotube is positioned on top of two 20-nm-thick gold leads using AFM manipulation. A rapid, 10-30 sec, heat treatment at 1000 K after the manipulation results in contact resistances of 10-20 kΩ. The 1/f α -noise is minimized in these free-standing constructions owing to the missing contact area with the SiO2 substrate insulator that contains trapping centers of charge. The measured equivalent background charge noise is in the range 2·10 −5 ... 6 · 10 −6 e/ √ Hz at frequencies 10 ... 45 Hz. Good noise properties seem to be connected with the increase of conductance observed near zero bias.
We have measured IV curves of multiwalled carbon nanotubes using end contacts. At low voltages, t... more We have measured IV curves of multiwalled carbon nanotubes using end contacts. At low voltages, the tunneling conductance obeys non-Ohmic power law, which is predicted both by the Luttinger liquid and the environment-quantum-fluctuation theories. However, at higher voltages we observe a crossover to Ohm's law with a Coulomb-blockade offset, which agrees with the environment-quantum-fluctuation theory, but cannot be explained by
We demonstrate high-contrast state detection of a superconducting flux qubit. Detection is realiz... more We demonstrate high-contrast state detection of a superconducting flux qubit. Detection is realized by probing the microwave transmission of a nonlinear resonator, based on a SQUID. Depending on the driving strength of the resonator, the detector can be operated in the monostable or the bistable mode. The bistable operation combines high-sensitivity with intrinsic latching. The measured contrast of Rabi oscillations is as high as 87 %; of the missing 13 %, only 3 % is unaccounted for. Experiments involving two consecutive detection pulses are consistent with preparation of the qubit state by the first measurement.
Phase dynamics has been measured in a driven mesoscopic Josephson oscillator where the resonance ... more Phase dynamics has been measured in a driven mesoscopic Josephson oscillator where the resonance is tuned either by magnetic flux or by gate charge modulation of the Josephson inductance. Phenomena are analyzed in terms of a "phase particle picture", and by numerical circuit simulations. An analogy to switching of a DC-biased junction into voltage state is discussed. Operation principle of the recently demonstrated Inductive Single-Electron Transistor (L-SET) based on the driven oscillator is reviewed. The obtained charge sensitivity implies that a performance comparable to the best rf-SETs has already been reached with the novel device.
Single electron transistors (SET) are fabricated from multiwalled carbon nanotubes (MWNT) by mani... more Single electron transistors (SET) are fabricated from multiwalled carbon nanotubes (MWNT) by manipulation with an atomic force microscope. The devices consist of either a single MWNT with Au contacts at the ends or of two crossing tubes. In the latter device, the lower nanotube acted as the central island of a single electron transistor while the upper one functioned as
We discuss how a single Cooper-pair transistor may be used to detect the superconducting phase di... more We discuss how a single Cooper-pair transistor may be used to detect the superconducting phase difference by using the phase dependence of the input capacitance from gate to ground. The proposed device has a low power dissipation because its operation is in principle free from quasiparticle generation. According to the sensitivity estimates, the device may be used for efficient qubit readout in a galvanically isolated and symmetrized circuit.
We demonstrate a sensitive method of charge detection based on radio-frequency readout of the Jos... more We demonstrate a sensitive method of charge detection based on radio-frequency readout of the Josephson inductance of a superconducting single-electron transistor. Charge sensitivity 1.4 ×10 4e/ √ Hz, limited by preamplifier, is achieved in an operation mode which takes advantage of the nonlinearity of the Josephson potential. Owing to reactive readout, our setup has more than two orders of magnitude lower dissipation than the existing method of radio-frequency elec- trometry. With an optimized sample, we expect uncoupled energy sensitivity below ~ in the same experimental scheme.
Using a classical equation of motion, dynamics of the phase is analyzed in the Inductive Single-E... more Using a classical equation of motion, dynamics of the phase is analyzed in the Inductive Single-Electron Transistor (L-SET) which is a promising new system suitable for quantum measurement with ultimate sensitivity and low back-action. In a regime of nonlinear dynamics, a shift of the oscillator resonant frequency is discovered which has a direct analogy to the switching of a dc-biased Josephson junction into voltage state. Results are reviewed for the predicted charge sensitivity, and it is shown that a performance challenging the best rf-SETs is foreseeable with the new device.
Low-frequency susceptibility of the split Cooper-pair box (SCPB) is investigated for use in sensi... more Low-frequency susceptibility of the split Cooper-pair box (SCPB) is investigated for use in sensitive measurements of external phase or charge. Depending on the coupling scheme, the box appears as either inductive or capacitive reactance which depends on external phase and charge. While coupling to the source-drain phase, we review how the SCPB looks like a tunable inductance, which property we used to build a novel radio-frequency electrometer. In the dual mode of operation, that is, while observed at the gate input, the SCPB looks like a capacitance. We concentrate on discussing the latter scheme, and we show how to do studies of fast phase fluctuations at a sensitivity of 1 mrad/ √ Hz by measuring the input capacitance of the box.
ABSTRACT We investigate the possibility of using multiwalled carbon nanotubes for constructing lo... more ABSTRACT We investigate the possibility of using multiwalled carbon nanotubes for constructing low-noise single-electron transistors (SETs). We use free-standing structures where the carbon nanotube is positioned on top of two 20-nm-thick gold leads using AFM manipulation. A rapid, 10-30 sec, heat treatment at 1000 K after the manipulation results in contact resistances of 10-20 kΩ. The 1/f α -noise is minimized in these free-standing constructions owing to the missing contact area with the SiO2 substrate insulator that contains trapping centers of charge. The measured equivalent background charge noise is in the range 2·10 −5 ... 6 · 10 −6 e/ √ Hz at frequencies 10 ... 45 Hz. Good noise properties seem to be connected with the increase of conductance observed near zero bias.
We have measured IV curves of multiwalled carbon nanotubes using end contacts. At low voltages, t... more We have measured IV curves of multiwalled carbon nanotubes using end contacts. At low voltages, the tunneling conductance obeys non-Ohmic power law, which is predicted both by the Luttinger liquid and the environment-quantum-fluctuation theories. However, at higher voltages we observe a crossover to Ohm's law with a Coulomb-blockade offset, which agrees with the environment-quantum-fluctuation theory, but cannot be explained by
We demonstrate high-contrast state detection of a superconducting flux qubit. Detection is realiz... more We demonstrate high-contrast state detection of a superconducting flux qubit. Detection is realized by probing the microwave transmission of a nonlinear resonator, based on a SQUID. Depending on the driving strength of the resonator, the detector can be operated in the monostable or the bistable mode. The bistable operation combines high-sensitivity with intrinsic latching. The measured contrast of Rabi oscillations is as high as 87 %; of the missing 13 %, only 3 % is unaccounted for. Experiments involving two consecutive detection pulses are consistent with preparation of the qubit state by the first measurement.
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Papers by L. Roschier