A non-invasive electron thermometer based on charge sensing of a quantum dot

Abstract

We present a thermometry scheme to extract the temperature of a 2DEG by monitoring the charge occupation of a weakly tunnel-coupled 'thermometer' quantum dot using a quantum point contact detector. Electronic temperatures between 97 mK and 307 mK are measured by this method with an accuracy of up to 3 mK, and agree with those obtained by measuring transport through a quantum dot. The thermometer does not pass a current through the 2DEG, and can be incorporated as an add-on to measure the temperature simultaneously with another operating device. Further, the tuning is independent of temperature.PACS numbers: 81.05. Ea,85.35.Gv,07.20.Dt,73.23.Hk,73.63.Kv The two-dimensional electron gas in GaAs/AlGaAs hetero-structures has diverse applications at cryogenic temperatures. For example, both gate-defined quantum dots and non-abelian fractional quantum hall states are candidates for a solid state quantum computer 1,2 . Almost all these applications require a low operating temperature, which is achieved by cooling the device using a dilution refrigerator or a helium-3 system. These external cooling mechanisms rely on the lattice cooling the electron gas via an exchange of phonons. In the mK range and lower, phonon coupling decreases with temperature, and this reduces the ability of external cooling mechanisms to cool the 2-DEG, limiting the minimum achievable temperature 3-5 . In practice, the electron gas is heated by unintended noise in the measurement set up to a temperature higher than the lattice. In many cases, the background electron temperature of an operating device is needed to analyze its behavior. This temperature has to be measured before or after the main experiment, an approach which cannot take into account any drift in electron temperature which occurs during the experiment. Our work describes the implementation of a thermometer which can perform an accurate and non-invasive temperature measurement 6,7 . The thermometer does not draw current from the sample being measured, which minimizes any back-action on the main experiment.Several low temperature thermometers have recently been realized using modern microlithography and nanolithography techniques 8 . For example, a fast NIS (normal metal-insulator-superconductor) junction thermometer, which operates at RF frequencies, has measured temperatures from 300 mK to 950 mK 9 . A 'Shot Noise Thermometer' (SNT) which extracts the electron temperature from the electrical shot noise through a tunneling junction between two metal electrodes has been shown to operate over a temperature range of 30 mK to 300 K with an accuracy of 0.1 % in the middle two decades of that range 10 . A 'Coulomb Blockade Thermometer' (CBT) a) am877@cam.ac.uk which relies on the temperature-dependent conductance of an array of tunneling junctions in an Al/Al 2 O 3 /Al structure, and which has an operating range of 20mK to tens of Kelvin with an absolute accuracy of 1% 11,12 , has been developed into a commercial product. The CBT can also operate in a magnetic field, which is an impor...

Fundamental aspects of steady-state conversion of heat to work at the nanoscale

“…1 Then the relaxation length will be much larger than the mean free path, and so it cannot be experimentally determined from the mobility. Instead, it must be measured by directly generating an out of equilibrium electron distribution, and studying how it relaxes to a thermal distribution [50][51][52]. In general the electron-electron scattering length scales with a lower power of temperature than the electronphonon scattering length, for details see [37,38].…”

Sensitive Radio-Frequency Measurements of a Quantum Dot by Tuning to Perfect Impedance Matching

“…2). The device under test is a laterally defined quantum dot [20] fabricated by patterning Ti=Au gates over a GaAs=AlGaAs heterostructure containing a two-dimensional electron gas (depth 90 nm, mobility 125 m 2 V −1 s −1 , carrier concentration 1.31 × 10 15 m −2 ). The device chip is bonded to a printed circuit board mounted with components of the matching circuit.…”

Silver-epoxy microwave filters and thermalizers for millikelvin experiments

“…We now turn to the filter performance measured by the device electron temperature T e with a GaAs quantum dot thermometer, [32][33][34][35][36][37][38][39][40] comparing T e with and without filters. For all measurements below, the sample wires are connected to the room temperature measurement setup through $1.5 m long thermo-coax cables, 41 which are very effective attenuators above a few GHz, see green curve in Fig.…”