Ultralow temperature nanorefrigerator Lattice Electrical environment Electron system G Cooling.

Ultralow temperature nanorefrigerator

Lattice

Electrical environment

Electron system

G

Cooling

NIS junction as a refrigerator

Optimum cooling power is reached at VC 2/e:

Cooling power of a NIS junction:

Temperature TN on the island is determined by the balance of heat fluxes, e.g.:

Electron-phonon heat flux: (dominates at high temperatures, negligible at low temperatures)

Optimum cooling power per junction, when superconducting reservoirs are not overheated, TS << TC

Efficiency (coefficient of performance) of a NIS junction refrigerator:

Experimental status

A. Clark et al., Appl. Phys. Lett. 86, 173508 (2005).

A. Luukanen et al., J. Low Temp. Phys. 120, 281 (2000).

Refrigeration of a membrane with separate thermometer

Refrigeration of a ”bulk” object

Nahum, Eiles, Martinis 1994 Demonstration of NIS coolingLeivo, Pekola, Averin 1996, Kuzmin 2003, Rajauria et al. 2007 Cooling electrons 300 mK -> 100 mK by SINISManninen et al. 1999 Cooling by SIS’IS see also Chi and Clarke 1979 and Blamire et al. 1991, Tirelli, Giazotto et al. 2008Manninen et al. 1997, Luukanen et al. 2000 Lattice (membrane) refrigeration by SINISSavin et al. 2001 S – Schottky – Semic – Schottky – S coolingClark et al. 2005, Miller et al. 2008 x-ray detector refrigerated by SINIS

For a review, see Rev. Mod. Phys. 78, 217 (2006).

Now:Temperature reduction (electrons): 300 mK -> 50 mKTemperature reduction (lattice): 200 mK -> 100 mKCooling power: 30 pW at 100 mK by one junction pair

Objectives (NanoFridge, EPSRC, Microkelvin):Electron cooling from 300 mK -> 10 mKCooled platform for nanosamples: 300 mK -> 50 mK, cooling power 10 nW at 100 mK by an array of junctionsCooler from 1.5 K down to 300 mK using higher Tc superconductor

Experiments in progress at TKK:Thermodynamic cycles with electrons: utilizing Coulomb blockade, heat pump with P = kBT f (proposal 2007)Refrigeration at the quantum limit (Meschke et al., Nature 2006, Timofeev et al. 2009, unpublished)Brownian refrigerator, Maxwell’s demon (proposal 2007)Cooling mechanical modes in suspended structures, i.e., nanomechanics combined with electronic refrigeration (Preliminary experiment, Muhonen et al. and Koppinen et al. 2009)

Specifications, objectives

JRA2

Ultralow temperature nanorefrigeratorTKK, CNRS, RHUL, SNS, BASEL, DELFT

Objectives Thermalizing and filtering electrons in nanodevicesTo 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

Roles of the participants

TKK and CNRS will develop the nanorefrigeration by superconducting tunnel junctionsSNS will build coolers based on semiconducting electron gasBASEL will work mainly on very low temperature thermalization and filtering DELFT and RHUL are mainly end users of the nano-coolers

Task 1: Thermalizing electrons in nanorefrigerators (TKK, CNRS, BASEL)

Ex-chip filtering:Sintered heat exchangers in a 3He cellLossy coaxes/strip lines, powder filters, ...

On-chip filtering:Lithographic resistive linesSQUID-arrays

W. Pan et al., PRL 83, 3530 (1999)

A. Savin et al., APL 91, 063512 2007

Task 2: Microkelvin nanocooler (TKK, CNRS, SNS)

Aim is to develop sub - 10 mK electronic cooler

Normal metal – superconductor tunnel junctions-based optimized coolers (TKK, CNRS, DELFT)

10 mK to lower T: Improved quality of tunnel junctionsThermometry at low T?Lower Tc superconductorQuasiparticle relaxation studies in sc and trapping of qp:s

Quantum dot cooler (SNS)

GaAs2DEG

ReservoirQD1 QD2

Drain Source

QD3

Therm.lead

GaAs 2DEG

Metallic split gates

VD

VTh

VS

V31

V33

V32

V11

V12

V13 V2

1

V22

V23

Thermometry at low T

SNS Josephson junction

Task 3: Development of a 100 mK, robust, electronically-cooled platform based on a 300

mK 3He bath (TKK, CNRS, RHUL, DELFT)

Commercial, robust SiN membranes (and custom made alumina) as platforms (TKK)Epitaxial large area junctions (CNRS)Optimized junctions (e-beam and mechanical masks)

RHUL and DELFT use these coolers for experiments on quantum devices

Deliverables

Task 1D1: Analysis of combined ex-chip and on-chip filter performance (18)D2: Demonstration of sub-10 mK electronic bath temperature of a nano-electronic tunnel junction device achieved by the developed filtering strategy (30)Task 2D3: Analysis of sub-10 mK nano-cooling techniques including (i) traditional N-I-S cooler with low Tc, (ii) quantum dot cooler (24)D4: Demonstration of sub-10 mK nanocooling with a N-I-S junction (48)Task 3D5: Demonstration of 300 mK to about 50 mK cooling of a dielectric platform (36)D6: Demonstration of cooling-based improved sensitivity of a quantum detector (48)