Eli Levenson-Falk

Distinct Signatures for Coulomb Blockade and Aharonov-Bohm Interference in Electronic Fabry-Perot Interferometers

Two distinct types of magnetoresistance oscillations are observed in two electronic Fabry-Perot interferometers of different sizes in the integer quantum Hall regime. Measuring these oscillations as a function of magnetic field and gate voltages, we describe three signatures that distinguish the two types. The oscillations observed in a

Approaching ideal weak link behavior with three dimensional aluminum nanobridges

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Fractional quantum Hall effect in a quantum point contact at filling fraction 5/2

device are understood to arise from a Coulomb blockade mechanism and those observed in an

Edge-State Velocity and Coherence in a Quantum Hall Fabry-Pérot Interferometer

18\text{ }\ensuremath{\mu}{\text{m}}^{2}

Nonlinear microwave response of aluminum weak-link Josephson oscillators

device from an Aharonov-Bohm mechanism. This work clarifies, provides ways to distinguish, and demonstrates control over these distinct mechanisms of oscillations seen in electronic Fabry-Perot interferometers.

In-plane magnetic field tolerance of a dispersive aluminum nanobridge SQUID magnetometer

We investigate unshunted dc superconducting quantum interference devices (SQUIDs) consisting of aluminum nanobridges of varying length L contacted with (two dimensional, or 2D) and (three dimensional, or 3D) banks. 3D nanobridge SQUIDs with L≤150 nm (approximately four times the superconducting coherence length) exhibit ≈70% critical current modulation with applied magnetic field, approaching the theoretical limit for an ideal short metallic weak link. In contrast, 2D nanobridge SQUIDs exhibit significantly lower critical current modulation. This enhanced nonlinearity makes 3D nanobridge Josephson junctions well suited to optimize sensitivity in weak link SQUID magnetometers as well as realize ultralow-noise amplifiers and qubits.

1/f noise of Josephson-junction-embedded microwave resonators at single photon energies and millikelvin temperatures

Recent theories suggest that the quasiparticles that populate certain quantum Hall states should exhibit exotic braiding statistics that could be used to build topological quantum gates. Confined systems that support such states at a filling fraction ν=5/2 are of particular interest for testing these predictions. Here, we report transport measurements of just such a system, which consists of a quantum point contact (QPC) in a two-dimensional GaAs/AlGaAs electron gas that itself exhibits a well-developed fractional quantum Hall effect at a bulk filling fraction νbulk=5/2. We observe plateau-like features at an effective filling fraction of νQPC=5/2 for lithographic contact widths of 1.2 μm and 0.8 μm, but not 0.5 μm. Transport near νQPC=5/2 in the QPCs is consistent with a picture of chiral Luttinger-liquid edge states with inter-edge tunnelling, suggesting that an incompressible state at νQPC=5/2 forms in this confined geometry.

Dispersive nanoSQUID magnetometry

We investigate nonlinear transport in electronic Fabry-Pérot interferometers in the integer quantum Hall regime. For interferometers sufficiently large that Coulomb blockade effects are absent, a checkerboardlike pattern of conductance oscillations as a function of dc bias and perpendicular magnetic field is observed. Edge-state velocities extracted from the checkerboard data are compared to model calculations and found to be consistent with a crossover from skipping orbits at low fields to E-vector x B-vector drift at high fields. Suppression of visibility as a function of bias and magnetic field is accounted for by including energy- and field-dependent dephasing of edge electrons.

Time Reversal Symmetry Breaking in the B Phase of the Heavy Fermion Superconductor PrOs

We present the driven response at T=30 mK of 6 GHz superconducting resonators constructed from capacitively-shunted three-dimensional (3D) aluminum nanobridge superconducting quantum interference devices (nanoSQUIDs). We observe flux modulation of the resonant frequency in quantitative agreement with numerical calculation and characteristic of near-ideal short weak-link junctions. Under strong microwave excitation, we observe stable bifurcation in devices with coupled quality factor (Q) ranging from 30–3500. Near this bias point, parametric amplification with >20 dB gain, 40 MHz bandwidth, and near quantum-limited noise performance is observed. Our results indicate that 3D nanobridge junctions are attractive circuit elements to realize quantum bits.

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We characterize the flux sensitivity of a dispersive 3D aluminum nanobridge SQUID magnetometer as a function of applied in-plane magnetic field. In zero field, we observe an effective flux noise of 17 n