Work package 2
Quantum standards/sensors within the SI
Task 1
Led by UPSaclay
Transport properties of the QAHE in MATBG
UPSaclay will fabricate single Hall bars made of MATBG and investigate, in collaboration with LNE
and CEA, the transport properties in the regime of the breakdown of the QAHE, as functions of
temperature and finite current, to determine how dissipation is emerging in the bulk, i.e. following
a thermal activation law or a variable-range hopping mechanism, as well as the corresponding energy
gaps. This will give insight in the physics of the QAHE in MATBG as well as the operating conditions
of the resistance standard.
Task 2
Led by LMU
Tunable Josephson devices made of MATBG
LMU will fabricate ultra-clean gate-defined single and arrays of Josephson junctions (JJs) and made
of MATBG and investigate their electronic properties as a function of gate voltage, which includes
detailed studies of the IcRn product, Fraunhofer patterns in magnetic field Ic(B) and the current-phase
relation. LMU and LNE will test the arrays, focusing on the AC Josephson effect by studing their
dynamics under RF irradiation, which is crucial for the development of the Josephson voltage standard.
For this, the JJs arrays will be irradiated by microwaves (20-70 GHz frequency range compatible with
equipment available at NMIs) and different couplings of the JJs to the microwaves will be tested.
Task 3
Led by LMU
Tunable SQUIDs made of MATBG
LMU will integrate gate-tunable JJs in a superconducting loop to form a SQUID in MATBG. Different
geometries with varying loop sizes will be tested. LMU and LNE will measure their magnetic response
through the flux-voltage transfer characteristics V (φ). A figure of merit of SQUIDs is given by the
transfer function Vφ = dV /dφ, that will be maximized for highest sensitivity by optimal tuning of the
gate voltages controlling the JJs’ barriers.
Task 4
Led by AMO
Interconnecting for On-chip PQCG
AMO will enable a programmable quantum current generator (PQCG) by providing interconnection
between a QAH device with a Josephson device on a single chip (provided by UPSaclay, LMU),
eventually from different stacks on a single wafer. The challenge will mainly reside in the interconnecting
schemes between devices to minimize parasitic resistances for accurate measurements. The design will
also enable external connection with a SQUID-based CCC.
Task 5
Led by CEA
Single-electron quantum current standard
CEA and UPSaclay will fabricate QAHE devices for on-demand electron source operating using
the QAHE. CEA will perform the experiments where Lorentzian pulses will generate pure electronic
excitations (Levitons) that will propagate along chiral edge states at zero-magnetic field. The accuracy
of the Leviton source will be characterized with shot-noise measurements.