25 research outputs found
Understanding the saturation power of Josephson Parametric Amplifiers made from SQUIDs arrays
We report on the implementation and detailed modelling of a Josephson
Parametric Amplifier (JPA) made from an array of eighty Superconducting QUantum
Interference Devices (SQUIDs), forming a non-linear quarter-wave resonator.
This device was fabricated using a very simple single step fabrication process.
It shows a large bandwidth (45 MHz), an operating frequency tunable between 5.9
GHz and 6.8 GHz and a large input saturation power (-117 dBm) when biased to
obtain 20 dB of gain. Despite the length of the SQUID array being comparable to
the wavelength, we present a model based on an effective non-linear LC series
resonator that quantitatively describes these figures of merit without fitting
parameters. Our work illustrates the advantage of using array-based JPA since a
single-SQUID device showing the same bandwidth and resonant frequency would
display a saturation power 15 dB lower.Comment: 12 pages, 9 figures, Appendices include
A photonic crystal Josephson traveling wave parametric amplifier
An amplifier combining noise performances as close as possible to the quantum
limit with large bandwidth and high saturation power is highly desirable for
many solid state quantum technologies such as high fidelity qubit readout or
high sensitivity electron spin resonance for example. Here we introduce a new
Traveling Wave Parametric Amplifier based on Superconducting QUantum
Interference Devices. It displays a 3 GHz bandwidth, a -102 dBm 1-dB
compression point and added noise near the quantum limit. Compared to previous
state-of-the-art, it is an order of magnitude more compact, its characteristic
impedance is in-situ tunable and its fabrication process requires only two
lithography steps. The key is the engineering of a gap in the dispersion
relation of the transmission line. This is obtained using a periodic modulation
of the SQUID size, similarly to what is done with photonic crystals. Moreover,
we provide a new theoretical treatment to describe the non-trivial interplay
between non-linearity and such periodicity. Our approach provides a path to
co-integration with other quantum devices such as qubits given the low
footprint and easy fabrication of our amplifier.Comment: 6 pages, 4 figures, Appendixe
Low-temperature quantum transport in CVD-grown single crystal graphene
Chemical vapor deposition (CVD) has been proposed for large-scale graphene
synthesis for practical applications. However, the inferior electronic
properties of CVD graphene are one of the key problems to be solved. In this
study, we present a detailed study on the electronic properties of high-quality
single crystal monolayer graphene. The graphene is grown by CVD on copper using
a cold-wall reactor and then transferred to Si/SiO2. Our low-temperature
magneto-transport data demonstrate that the characteristics of the measured
single-crystal CVD graphene samples are superior to those of polycrystalline
graphene and have a quality which is comparable to that of exfoliated graphene
on Si/SiO2. The Dirac point in our best samples is located at back-gate
voltages of less than 10V, and their mobility can reach 11000 cm2/Vs. More than
12 flat and discernible half-integer quantum Hall plateaus have been observed
in high magnetic field on both the electron and hole side of the Dirac point.
At low magnetic field, the magnetoresistance shows a clear weak localization
peak. Using the theory of McCann et al., we find that the inelastic scattering
length is larger than 1 {\mu}m in these samples even at the charge neutrality
point
Low-temperature quantum transport in CVD-grown single crystal graphene
Chemical vapor deposition (CVD) is typically used for large-scale graphene synthesis for practical applications. However, the inferior electronic properties of CVD graphene are one of the key problems to be solved. Therefore, we present a detailed study on the electronic properties of high-quality single-crystal monolayer graphene. The graphene is grown via CVD on copper, by using a cold-wall reactor, and then transferred to Si/SiO2. Our low-temperature magneto-transport data demonstrate that the characteristics of the single-crystal CVD graphene samples are superior to those of polycrystalline graphene and have a quality which is comparable to that of exfoliated graphene on Si/SiO2. The Dirac point in our best samples occurs at back-gate voltages lower than 10 V, and a maximum mobility of 11,000 cm2/(V·s) is attained. More than 12 flat and discernible half-integer quantum Hall plateaus occur under a high magnetic field on both the electron and hole sides of the Dirac point. At a low magnetic field, the magnetoresistance exhibits a weak localization peak. Using the theory of McCann et al., we obtain inelastic scattering lengths of >1 µm, even at the charge neutrality point of the samples
Observation of two-mode squeezing in a traveling wave parametric amplifier
Traveling wave parametric amplifiers (TWPAs) have recently emerged as
essential tools for broadband near quantum-limited amplification. However,
their use to generate microwave quantum states still misses an experimental
demonstration. In this letter, we report operation of a TWPA as a source of
two-mode squeezed microwave radiation. We demonstrate broadband entanglement
generation between two modes separated by up to 400 MHz by measuring
logarithmic negativity between 0.27 and 0.51 and collective quadrature
squeezing below the vacuum limit between 1.5 and 2.1 dB. This work opens
interesting perspectives for the exploration of novel microwave photonics
experiments with possible applications in quantum sensing and continuous
variable quantum computing
A tunable Josephson platform to explore many-body quantum optics in circuit-QED
Coupling an isolated emitter to a single mode of the electromagnetic field is
now routinely achieved and well understood. Current efforts aim to explore the
coherent dynamics of emitters coupled to several electromagnetic modes (EM).
freedom. Recently, ultrastrong coupling to a transmission line has been
achieved where the emitter resonance broadens to a significant fraction of its
frequency. In this work we gain significantly improved control over this
regime. We do so by combining the simplicity of a transmon qubit and a bespoke
EM environment with a high density of discrete modes, hosted inside a
superconducting metamaterial. This produces a unique device in which the
hybridisation between the qubit and up to 10 environmental modes can be
monitored directly. Moreover the frequency and broadening of the qubit
resonance can be tuned independently of each other in situ. We experimentally
demonstrate that our device combines this tunability with ultrastrong coupling
and a qubit nonlinearity comparable to the other relevant energy scales in the
system. We also develop a quantitative theoretical description that does not
contain any phenomenological parameters and that accurately takes into account
vacuum fluctuations of our large scale quantum circuit in the regime of
ultrastrong coupling and intermediate non-linearity. The demonstration of this
new platform combined with a quantitative modelling brings closer the prospect
of experimentally studying many-body effects in quantum optics. A limitation of
the current device is the intermediate nonlinearity of the qubit. Pushing it
further will induce fully developed many-body effects, such as a giant Lamb
shift or nonclassical states of multimode optical fields. Observing such
effects would establish interesting links between quantum optics and the
physics of quantum impurities.Comment: Main paper and Supplementary Information combined in one file. List
of the modifications in the final version: new abstract and introduction,
comparison to RWA treatment, more precise capacitance mode
Fabrication and characterization of aluminum SQUID transmission lines
We report on the fabrication and characterization of 50 Ohms, flux-tunable,
low-loss, SQUID-based transmission lines. The fabrication process relies on the
deposition of a thin dielectric layer (few tens of nanometers) via Atomic Layer
Deposition (ALD) on top of a SQUID array, the whole structure is then covered
by a non-superconducting metallic top ground plane. We present experimental
results from five different samples. We systematically characterize their
microscopic parameters by measuring the propagating phase in these structures.
We also investigate losses and discriminate conductor from dielectric losses.
This fabrication method offers several advantages. First, the SQUID array
fabrication does not rely on a Niobium tri-layer process but on a simpler
double angle evaporation technique. Second, ALD provides high quality
dielectric leading to low-loss devices. Further, the SQUID array fabrication is
based on a standard, all-aluminum process, allowing direct integration with
superconducting qubits. Moreover, our devices are in-situ flux tunable,
allowing mitigation of incertitude inherent to any fabrication process.
Finally, the unit cell being a single SQUID (no extra ground capacitance is
needed), it is straightforward to modulate the size of the unit cell
periodically, allowing band-engineering. This fabrication process can be
directly applied to traveling wave parametric amplifiers.Comment: 9 pages, 9 figures, Appendixe
State preparation of a fluxonium qubit with feedback from a custom FPGA-based platform
We developed a versatile integrated control and readout instrument for
experiments with superconducting quantum bits (qubits), based on a
field-programmable gate array (FPGA) platform. Using this platform, we perform
measurement-based, closed-loop feedback operations with
platform latency. The feedback capability is instrumental in realizing active
reset initialization of the qubit into the ground state in a time much shorter
than its energy relaxation time . We show experimental results
demonstrating reset of a fluxonium qubit with fidelity, using a
readout-and-drive pulse sequence approximately long.
Compared to passive ground state initialization through thermalization, with
the time constant given by , the use of the
FPGA-based platform allows us to improve both the fidelity and the time of the
qubit initialization by an order of magnitude.Comment: 3 pages, 2 figures. The following article has been submitted to the
AIP Conference Proceedings of the Fifth International Conference on Quantum
Technologies (ICQT-2019
Broadband parametric amplification for multiplexed SiMOS quantum dot signals
Spins in semiconductor quantum dots hold great promise as building blocks of
quantum processors. Trapping them in SiMOS transistor-like devices eases future
industrial scale fabrication. Among the potentially scalable readout solutions,
gate-based dispersive radiofrequency reflectometry only requires the already
existing transistor gates to readout a quantum dot state, relieving the need
for additional elements. In this effort towards scalability, traveling-wave
superconducting parametric amplifiers significantly enhance the readout
signal-to-noise ratio (SNR) by reducing the noise below typical cryogenic
low-noise amplifiers, while offering a broad amplification band, essential to
multiplex the readout of multiple resonators. In this work, we demonstrate a
3GHz gate-based reflectometry readout of electron charge states trapped in
quantum dots formed in SiMOS multi-gate devices, with SNR enhanced thanks to a
Josephson traveling-wave parametric amplifier (JTWPA). The broad, tunable 2GHz
amplification bandwidth combined with more than 10dB ON/OFF SNR improvement of
the JTWPA enables frequency and time division multiplexed readout of interdot
transitions, and noise performance near the quantum limit. In addition, owing
to a design without superconducting loops and with a metallic ground plane, the
JTWPA is flux insensitive and shows stable performances up to a magnetic field
of 1.2T at the quantum dot device, compatible with standard SiMOS spin qubit
experiments
Non-degenerate parametric amplifiers based on dispersion engineered Josephson junction arrays
Determining the state of a qubit on a timescale much shorter than its
relaxation time is an essential requirement for quantum information processing.
With the aid of a new type of non-degenerate parametric amplifier, we
demonstrate the continuous detection of quantum jumps of a transmon qubit with
90% fidelity in state discrimination. Entirely fabricated with standard
two-step optical lithography techniques, this type of parametric amplifier
consists of a dispersion engineered Josephson junction (JJ) array. By using
long arrays, containing JJs, we can obtain amplification at multiple
eigenmodes with frequencies below , which is the typical range
for qubit readout. Moreover, by introducing a moderate flux tunability of each
mode, employing superconducting quantum interference device (SQUID) junctions,
a single amplifier device could potentially cover the entire frequency band
between 1 and .Comment: P.W. and I.T. contributed equally. 9 pages, 5 figures and appendice