46 research outputs found
The Time Structure of Hadronic Showers in Calorimeters with Scintillator and with Gas Readout
Hadronic showers are characterized by a rich particle structure in the
spatial as well as in the time domain. The prompt component comes from
relativistic fragments that deposit energy at the ns scale, while late
components are associated predominantly with neutrons in the cascade. To
measure the impact of these late components, two experiments, based on gaseous
and plastic active layers with steel and tungsten absorbers, were set up. The
different choice for the material of the active layers produces distinct
responses to neutrons, and consequently to late energy depositions. After
discussing the technical aspects of these systems, we present a comparison of
the signals, read out with fast digitizers with deep buffers, and provide
detailed information of the time structure of hadronic showers over a long
sampling window.Comment: proceeding for CALOR2014, 6 pages, 5 figure
A time resolved study of injection backgrounds during the first commissioning phase of SuperKEKB
We report on measurements of beam backgrounds during the first commissioning
phase of the SuperKEKB collider in 2016, performed with the plastic
scintillator and silicon photomultiplier-based CLAWS detector system. The
sub-nanosecond time resolution and single particle detection capability of the
sensors allow bunch-by-bunch measurements, enable CLAWS to perform a novel time
resolved analysis of beam backgrounds, and make the system uniquely suited for
the study of injection backgrounds. We present measurements of various aspects
of regular beam background and injection backgrounds which include time
structure and decay behavior of injection backgrounds, hit-energy spectra and
overall background rates. These measurements show that the elevated background
rates following an injection generally last for several milliseconds, with the
majority of the background particles typically observed within the first 500
us. The injection backgrounds exhibit pronounced patterns in time, connected to
betatron and synchrotron oscillations in the accelerator rings. The frequencies
of these patterns are determined from detector data.Comment: 19 pages, 12 figures, published in EPJ
Readout of a quantum processor with high dynamic range Josephson parametric amplifiers
We demonstrate a high dynamic range Josephson parametric amplifier (JPA) in
which the active nonlinear element is implemented using an array of rf-SQUIDs.
The device is matched to the 50 environment with a Klopfenstein-taper
impedance transformer and achieves a bandwidth of 250-300 MHz, with input
saturation powers up to -95 dBm at 20 dB gain. A 54-qubit Sycamore processor
was used to benchmark these devices, providing a calibration for readout power,
an estimate of amplifier added noise, and a platform for comparison against
standard impedance matched parametric amplifiers with a single dc-SQUID. We
find that the high power rf-SQUID array design has no adverse effect on system
noise, readout fidelity, or qubit dephasing, and we estimate an upper bound on
amplifier added noise at 1.6 times the quantum limit. Lastly, amplifiers with
this design show no degradation in readout fidelity due to gain compression,
which can occur in multi-tone multiplexed readout with traditional JPAs.Comment: 9 pages, 8 figure
Measurement-Induced State Transitions in a Superconducting Qubit: Within the Rotating Wave Approximation
Superconducting qubits typically use a dispersive readout scheme, where a
resonator is coupled to a qubit such that its frequency is qubit-state
dependent. Measurement is performed by driving the resonator, where the
transmitted resonator field yields information about the resonator frequency
and thus the qubit state. Ideally, we could use arbitrarily strong resonator
drives to achieve a target signal-to-noise ratio in the shortest possible time.
However, experiments have shown that when the average resonator photon number
exceeds a certain threshold, the qubit is excited out of its computational
subspace, which we refer to as a measurement-induced state transition. These
transitions degrade readout fidelity, and constitute leakage which precludes
further operation of the qubit in, for example, error correction. Here we study
these transitions using a transmon qubit by experimentally measuring their
dependence on qubit frequency, average photon number, and qubit state, in the
regime where the resonator frequency is lower than the qubit frequency. We
observe signatures of resonant transitions between levels in the coupled
qubit-resonator system that exhibit noisy behavior when measured repeatedly in
time. We provide a semi-classical model of these transitions based on the
rotating wave approximation and use it to predict the onset of state
transitions in our experiments. Our results suggest the transmon is excited to
levels near the top of its cosine potential following a state transition, where
the charge dispersion of higher transmon levels explains the observed noisy
behavior of state transitions. Moreover, occupation in these higher energy
levels poses a major challenge for fast qubit reset