Tunnel-Junction Thermometry Down to Millikelvin Temperatures

Feshchenko, A. V.; Casparis, Lucas; Khaymovich, Ivan M.; Maradan, Dario; Saira, Olli-Pentti; Palma, Mario; Meschke, Matthias; Pekola, Jukka P.; Zumbühl, Dominik M.

doi:10.1103/physrevapplied.4.034001

Cited by 55 publications

(61 citation statements)

References 47 publications

(75 reference statements)

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“…To account for these challenges special care was taken on damping all connections to the fridge and decoupling the PT cold head 21 from the rest of the system. The presented setup was improved from a previous wet system 6,7 to particularly meet the demands of a cryogen-free system 21 . We introduced a rigid support structure and an adapted geometry of the NRs.…”

Section: Nuclear Refrigerator Network Onmentioning

confidence: 99%

“…In many laboratories, the sample is only weakly coupled to the coldest spot of the refrigerator, resulting in sample temperatures significantly higher than the base temperature of the refrigerator. In order to efficiently couple sample and refrigerator, a parallel network of Nuclear Refrigerators (NRs) was proposed 6,7 , where every lead is well thermalized through the mixing chamber (MC) and has its own NR. Our approach relies on the Wiedemann-Franz cooling of the conduction electrons 8 , which is the main cooling mechanism in the mK-regime and below.…”

Section: Introductionmentioning

confidence: 99%

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Magnetic cooling for microkelvin nanoelectronics on a cryofree platform

Palma

Maradan

Casparis

et al. 2017

Review of Scientific Instruments

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We present a parallel network of 16 demagnetization refrigerators mounted on a cryofree dilution refrigerator aimed to cool nanoelectronic devices to sub-millikelvin temperatures. To measure the refrigerator temperature, the thermal motion of electrons in a Ag wirethermalized by a spot-weld to one of the Cu nuclear refrigerators -is inductively picked-up by a superconducting gradiometer and amplified by a SQUID mounted at 4 K. The noise thermometer as well as other thermometers are used to characterize the performance of the system, finding magnetic field independent heat-leaks of a few nW/mol, cold times of several days below 1 mK, and a lowest temperature of 150 µK of one of the nuclear stages in a final field of 80 mT, close to the intrinsic SQUID noise of about 100 µK. A simple thermal model of the system capturing the nuclear refrigerator, heat leaks, as well as thermal and Korringa links describes the main features very well, including rather high refrigerator efficiencies typically above 80 %.

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Section: Nuclear Refrigerator Network Onmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Magnetic cooling for microkelvin nanoelectronics on a cryofree platform

Palma

Maradan

Casparis

et al. 2017

Review of Scientific Instruments

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“…Each wire is cooled by its own, separate nuclear refrigerator in form of a large Cu plate. However, despite recent progress [18][19][20][21][22][23][24][25] , it remains very challenging to cool nanostructures even below 10 mK. Due to reduced thermal coupling, these samples are extremely susceptible to heat leaks such as vibrations 25 , microwave radiation 26,27 , heat release 17 and electronic noise 20 .…”

mentioning

confidence: 99%

“…Due to reduced thermal coupling, these samples are extremely susceptible to heat leaks such as vibrations 25 , microwave radiation 26,27 , heat release 17 and electronic noise 20 . Metallic Coulomb blockade thermometers (CBTs) have been established as precise and reliable electronic thermometers 18,28,29 , operating down to 10 mK and slightly below 21,22,24,30 . These typically consist of linear arrays of Al/AlO x /Al tunnel junctions with metallic islands in-between, consisting mainly of copper, see Fig.…”

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confidence: 99%

On-and-off chip cooling of a Coulomb blockade thermometer down to 2.8 mK

Palma

Scheller

Maradan

et al. 2017

Applied Physics Letters

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Cooling nanoelectronic devices below 10 mK is a great challenge since thermal conductivities become very small, thus creating a pronounced sensitivity to heat leaks. Here, we overcome these difficulties by using adiabatic demagnetization of both the electronic leads and the large metallic islands of a Coulomb blockade thermometer. This reduces the external heat leak through the leads and also provides on-chip refrigeration, together cooling the thermometer down to 2.8 ± 0.1 mK. We present a thermal model which gives a good qualitative account and suggests that the main limitation is heating due to pulse tube vibrations. With better decoupling, temperatures below 1 mK should be within reach, thus opening the door for μK nanoelectronics.

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“…The rate decreases exponentially with decreasing temperature, indicating a thermally activated process, until a background rate as described before is reached, giving an upper limit to the electron temperature. The exponential decay is potentially useful for thermometry [28], and again suggests involvement of the reservoirs with their exponential tails of the Fermi-Dirac distributions. At elevated temperatures, the switching rate exceeds the sensor bandwidth, rendering the switching diamond invisible [29].…”

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confidence: 99%

Intrinsic Metastabilities in the Charge Configuration of a Double Quantum Dot

et al. 2015

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We report a thermally activated metastability in a GaAs double quantum dot exhibiting real-time charge switching in diamond shaped regions of the charge stability diagram. Accidental charge traps and sensor backaction are excluded as the origin of the switching. We present an extension of the canonical double dot theory based on an intrinsic, thermal electron exchange process through the reservoirs, giving excellent agreement with the experiment. The electron spin is randomized by the exchange process, thus facilitating fast, gate-controlled spin initialization. At the same time, this process sets an intrinsic upper limit to the spin relaxation time. DOI: 10.1103/PhysRevLett.115.106804 PACS numbers: 73.21.La, 73.23.Hk, 73.63.Kv Spins in quantum dots [1] are promising candidates for the realization of qubits-the elementary units of a quantum computer. Great progress was made in recent years towards implementing quantum information processing schemes with electron spins in GaAs quantum dots [2][3][4][5][6][7][8], which hold the potential for scaling to a large number of qubits [9][10][11]. Stable qubits with long coherence times are of crucial importance to execute numerous coherent quantum gates. Spin echo and dynamical decoupling techniques were successfully employed to isolate the electronic system from the slowly fluctuating nuclear spins of the GaAs host material [3,[12][13][14][15], enhancing the coherence time T 2 from below 1 μs to much longer times exceeding 0.2 ms. A fundamental limit T 2 ≤ 2T 1 is set by the spin relaxation time T 1 . In a magnetic field, spins relax through spin-phonon coupling mediated by the spin-orbit interaction [2,[16][17][18]. Since here the spin-orbit coupling is weak, very long T 1 times result, exceeding 1 s at 1 T [19], leaving ample room for further improvements of the spin qubit coherence.In this Letter, we report the experimental observation of a thermal electron exchange process via the reservoirs of a quantum dot, setting an intrinsic upper bound to T 1 , which can be orders of magnitude lower than the fundamental spin-phonon limit [16]. The resulting metastable charge states-appearing in the double dot (DD) in the absence of interdot tunneling-make the exchange process detectable with a charge sensor. Within a diamond shaped region, the DD switches its charge state back and forth over time from an electron on the left dot to an electron on the right dot without direct interdot tunneling. After excluding unintentional charge traps and sensor backaction, we present an extension of the orthodox DD transport theory accounting very well for the observations. The exchange process can be used for fast qubit initialization [7]. Finally, we outline ways to extend T 1 up to the spin-phonon limit.The sample is fabricated from a GaAs heterostructure with a 2D electron gas 110 nm below the surface (density 2.6 × 10 11 cm −2 and mobility 4 × 10 5 cm 2 =V s). The device layout, see Fig. 1(a), is adopted from Ref. [20]. Each dot adjacent to the DD (center) acts as a charge sensor [...

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Tunnel-Junction Thermometry Down to Millikelvin Temperatures

Cited by 55 publications

References 47 publications

Magnetic cooling for microkelvin nanoelectronics on a cryofree platform

Magnetic cooling for microkelvin nanoelectronics on a cryofree platform

On-and-off chip cooling of a Coulomb blockade thermometer down to 2.8 mK

Intrinsic Metastabilities in the Charge Configuration of a Double Quantum Dot

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