Josephson regelbare Metamaterialien für Quantenbauelemente

01/01/2021 to 31/12/2023

Presently there is a growing interest in development of quantum devices (qubits, detectors, etc.) that, due to
their nature, operate at low and ultra low temperatures and at frequencies of several (tens of) GHz. Therefore,
the design of functional metamaterials (filters, amplifiers, and so on) that operate at the same temperatures
and frequencies and allow to control, process and readout of the information as well as amplify weak quantum
signals is very relevant. Superconductivity brings unique advantages to metamaterials such as low loss,
compact dimensions of meta-atoms, while the Josephson effect provides the possibility to tune metamaterial
properties in-situ.
In the framework of this joint project we are going to design, fabricate and investigate both theoretically
(numerically) and experimentally several metamaterials based on arrays of meta-atoms, such as Josephson
junctions (JJs) or SQUIDs, embedded into coplanar transmission line. The T¨ubingen group will focus on the
development of novel Josephson MetaMaterials (JMMs) with unique and tunable properties. In the linear
regime the aim is to design a JMM with the tunable dispersion that allows to create, e.g., JMM that works as
a tunable band-pass or band-rejection filter or, e.g., JMMs with zero group velocity, where the propagating
electromagnetic waves can be stopped.
The main focus of the Moscow group is more application oriented. It is the development and experimental
tests of the Josephson Traveling Wave Parametric Amplifier (JTWPA) — a JMM working in a non-linear
regime, where non-linear mixing of a weak input signal (to be amplified) at the signal frequency with the
strong pump signal at pump frequency results in an amplified signal at the signal frequency at the output
of the JTWPA. The theory predicts that a JTWPA consisting of 300 SQUIDs should provide a uniform gain
of 20 dB over the bandwidth of about 5 GHz at the pump frequency of 12 GHz. The noise temperature is
expected to reach 0.2 K at 5 GHz at a temperature of 4.2K. At the later stage of the project the JTWPA will
be redesigned for temperatures below 1K.
The T¨ubingen group will also investigate JMMs experimentally by means of Low Temperature Scanning
Electron (or Laser) Microscopy (LTSEM/LTSLM) – a unique technique available in T¨ubingen. After upgrade,
it will allow to visualize the operation of the JMMs such as JTWPA and find the problem areas if any. In this
context an important point is to understand how the deviation of parameters of (a) one single meta-atom
(important for LTSEM/LTSLM imaging) or (b) all meta-atoms (technological spread) affect the operation and figures of merit of JMM. The group in T¨ubingen will investigate this question by making full scale non-linear
numerical simulations of JMM dynamics.
Finally, novel JMMs designed by the T¨ubingen group will be fabricated in Moscow and experimentally investigated
by both groups.