JRA2 Ultralow temperature nanorefrigerator AALTO, CNRS, RHUL,
SNS, BASEL, DELFT Objectives Thermalizing and filtering electrons
in nanodevices To develop an electronic nano-refrigerator that is
able to reach sub-10 mK electronic temperatures To develop an
electronic microrefrigerator for cooling galvanically isolated
nanosamples AALTO and CNRS will develop the nanorefrigeration by
superconducting tunnel junctions SNS will build coolers based on
semiconductors (quantum wires, quantum dots) BASEL will work on
very low temperature thermalization and ex-chip filtering DELFT and
RHUL are end users of the nano-coolers
Slide 2
Deliverables and milestones Task 1 D1: Analysis of combined
ex-chip and on-chip filter performance (18) DONE D2: Demonstration
of sub-10 mK electronic bath temperature of a nano-electronic
tunnel junction device achieved by the developed filtering strategy
(30) IN PROGRESS M1: Choice of the thermalization strategy
(sintered heat exchangers, 3 He cell) (12) done M2: Choice of the
ex-chip filtering technique (18) done Task 2 D3: Analysis of sub-10
mK nano-cooling techniques including (i) traditional N-I-S cooler
with low Tc, (ii) quantum dot cooler (24) IN PROGRESS, PARTLY DONE
D4: Demonstration of sub-10 mK nanocooling with a N-I-S junction
(48) PLANNED M3: Choice of the superconductor material with a lower
critical temperature (24) ? M4: Precise definition of the QD cooler
geometry and materials (24) ? Task 3 D5: Demonstration of 300 mK to
about 50 mK cooling of a dielectric platform (36) IN PROGRESS D6:
Demonstration of cooling-based improved sensitivity of a quantum
detector (48) (DONE!) M5: Design of the membrane patterning and of
the micro-coolers, based on heat and quasiparticles diffusion
calculations (18) done M6: Delivery of the first membranes to the
end users (36) done
Slide 3
Task 1: Thermalizing electrons in nanorefrigerators (AALTO,
CNRS, BASEL) Ex-chip filtering: Sintered heat exchangers in a 3He
cell Lossy coaxes/strip lines, powder filters,... On-chip
filtering: Lithographic on-chip filtering W. Pan et al., PRL 83,
3530 (1999) A. Savin et al., APL 91, 063512 2007
Slide 4
Environment (i.e., photon) assisted tunneling in a NIS junction
Tunneling rates are affected by the hot environment. This can be
treated using the P(E) theory accounting for fluctuations at a
junction. Filtering, low T Hot 4 K environment, R env R = R env
Typically: R env = 100 R < 1 Junction eV PHOTON ABSORPTION and
TUNNELING
Slide 5
PAT has the same effect as Dynes density of states with PRL
105, 026803 (2010) Experimental data fits well with the assumption
of lifetime-broadened DOS. Theory yields a 1-1 correspondence
assuming weakly dissipative high T environment. Improved
characteristics of quantized current plateaus
Slide 6
Device Electron Temperature: with microwave filters With
microwave filters: T MC = 5 mK, T E = 18 2 mK for GaAs CBT and
about13 mK for metallic CBT (preliminary result for the metallic
device)
Slide 7
D1: Analysis of combined ex-chip and on-chip filter performance
(18) DONE Capacitive and resistive on-chip filters tested, and they
perform well up to f >> 50 GHz (4 K). Theoretically RC
on-chip filter would be even better and this can be easily
fabricated as well. Ex-chip filters: Thermocoax cable (high f
filtering) Miniature silver-epoxy microwave filters (low f
filtering, down to a few MHz) Thermalizing of the wires by sintered
silver heat exchangers located in the 3He/4He mixture D2:
Demonstration of sub-10 mK electronic bath temperature of a
nano-electronic tunnel junction device achieved by the developed
filtering strategy (30) IN PROGRESS Electronic temperatures of
quantum dot and metallic CBT:s down to 18 (10) mK Tests of ultimate
performance in progress -> Dominik Zumbuhls talk M1: Choice of
the thermalization strategy (sintered heat exchangers, 3 He cell)
(12) done M2: Choice of the ex-chip filtering technique (18)
done
Slide 8
Task 2: Microkelvin nanocooler (AALTO, CNRS, SNS) Aim is to
develop sub - 10 mK electronic cooler Normal metal superconductor
tunnel junctions-based optimized coolers (AALTO, CNRS, DELFT)
Towards lower T: Improved quality of tunnel junctions? Thermometry
at low T? Lower Tc superconductor Quasiparticle relaxation studies
in sc and trapping of qp:s Quantum dot cooler (SNS)
Slide 9
D3: Analysis of sub-10 mK nano-cooling techniques including (i)
traditional NIS cooler with low Tc, (ii) quantum dot cooler (24) IN
PROGRESS, PARTLY DONE D4: Demonstration of sub-10 mK nanocooling
with a NIS junction (48) PLANNED D3 (i): AlMn-Ti NIS junction. AlMn
is normal, Ti superconducting with Tc = 0.4 K (cf. Al Tc = 1.2 K in
thin films). Junctions are good for thermometry but no cooling was
observed.
Slide 10
D3: Analysis of sub-10 mK nano-cooling techniques including (i)
traditional NIS cooler with low Tc, (ii) quantum dot cooler (24) IN
PROGRESS, PARTLY DONE D4: Demonstration of sub-10 mK nanocooling
with a NIS junction (48) PLANNED D3 (i): Standard NIS junction
cooler in small perpendicular to film magnetic field (few G).
Performance improved, probably thanks to enhanced quasiparticle
relaxation in Al superconductor. Theoretical analysis in
progress.
Slide 11
D3: Analysis of sub-10 mK nano-cooling techniques including (i)
traditional NIS cooler with low Tc, (ii) quantum dot cooler (24) IN
PROGRESS, PARTLY DONE D4: Demonstration of sub-10 mK nanocooling
with a NIS junction (48) PLANNED D3 (ii): GaAs/AlGaAs 2DEG cooler
(SNS Pisa). Thermometry by quantum dot CBTs. Quasiparticle energy
relaxation in the central area either by electron-phonon coupling
(high T) or through the quantum dot (low T). Optimized cooler to be
developed. arXiv:1007.0172, submitted.
Slide 12
Task 3: Development of a 100 mK, robust, electronically-cooled
platform based on a 300 mK 3He bath (AALTO, CNRS, RHUL, DELFT)
Commercial, robust SiN membranes (or custom made alumina?) as
platforms (AALTO) Epitaxial large area junctions (CNRS) Optimized
junctions (e-beam and mechanical masks) RHUL and DELFT use these
coolers for experiments on quantum devices
Slide 13
Task 3 D5: Demonstration of 300 mK to about 50 mK cooling of a
dielectric platform (36) IN PROGRESS D6: Demonstration of
cooling-based improved sensitivity of a quantum detector (48)
(DONE!) M5: Design of the membrane patterning and of the
micro-coolers, based on heat and quasiparticles diffusion
calculations (18) done M6: Delivery of the first membranes to the
end users (36) done Two-stage photolithography for large area
cooler junctions in progress at CNRS. M5: CAD-design and
experimental tests of membrane coolers done. Performance still poor
(few mK cooling only)
Slide 14
Task 3 D5: Demonstration of 300 mK to about 50 mK cooling of a
dielectric platform (36) IN PROGRESS D6: Demonstration of
cooling-based improved sensitivity of a quantum detector (48)
(DONE!) M5: Design of the membrane patterning and of the
micro-coolers, based on heat and quasiparticles diffusion
calculations (18) done M6: Delivery of the first membranes to the
end users (36) done M6, D6: Delft-Aalto: Combining a membrane
cooler with a KID- detector. Improved KID performance demonstrated
(N. Vercruyssen talk). RHUL-Aalto collaboration: SIS- junctions on
membranes fabricated.
Slide 15
Achievements by July 2010 Task 1: AALTO: On-chip filtering
suppresses significantly leakage and dissipation in NIS junctions
theoretical model developed and experimental demonstration
performed BASEL: Sophisticated microwave ex-chip filtering
demonstrates electron temperature of 18 mK Task 2: SNS: Quantum dot
thermometry and thermal transport measurements performed AALTO:
AlMn as a normal material tested for cooler purposes CNRS: Electron
and phonon temperatures measured separately Task 3: CNRS: Epitaxial
large tunnel junction process under way AALTO: Coolers on silicon
nitride membranes produced, cooling power degraded in the first
experiments by poor efficiency of the cold finger DELFT: Kinetic
inductance detector fabricated and demonstrated (performance
improvement by cooling) on a platform produced by AALTO RHUL: Tests
of Josephson junctions on cooler platforms (together with AALTO) 5
or more articles on JRA2 either published, submitted or under
preparation for publication
Slide 16
BASEL: Filtering Strategy: Stage 1 Thermocoax cables from room
T to 10 mK 1.5 meters attenuation > 100 dB for f > 4 GHz Uni
Basel, Zumbhl groupJRA2, filtering & thermalizing
Slide 17
Stage 2: Cryogenic Miniature Microwave Filters attenuation >
100 dB for f > 150 MHz attenuation > 100 dB for f > 20 MHz
mounted @ 10 mK Uni Basel, Zumbhl groupJRA2, filtering &
thermalizing
Slide 18
Stage 2: Cryogenic Miniature Microwave Filters RT, LN 2 and LHe
attenuation no significant degradation of performance at 4 K Uni
Basel, Zumbhl groupJRA2, filtering & thermalizing
Slide 19
GaAs Quantum Dot Electron Thermometer 500 nm Use GaAs quantum
dot as a thermometer (Coulomb blockade) differential conductance or
DC current temperature broadened regime (