4 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
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