Metallic Coulomb blockade thermometry down to 10 mK and below

Casparis, Lucas; Meschke, Matthias; Maradan, Dario; Clark, Anthony C.; Scheller, Christian; Schwarzwälder, Kai Kurt; Pekola, Jukka P.; Zumbühl, Dominik M.

doi:10.1063/1.4744944

Cited by 33 publications

(59 citation statements)

References 18 publications

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“…The experiment was done in a dilution refrigerator at base temperature T ∼ 20 mK. Ag-epoxy microwave filters and thermalizers [23] are mounted at the mixing chamber for improved cooling [24,25], giving an electron temperature of T e ∼ 60 mK from Coulomb blockade thermometry [26]. All data presented here were acquired with the left sensor dot, though the right sensor gives essentially the same results.…”

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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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Intrinsic Metastabilities in the Charge Configuration of a Double Quantum Dot

et al. 2015

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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 .…”

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“…The conductance g 0 measured while permanently staying at zero bias 37 is clearly lower in conductance (dark blue marker) -and thus also lower in temperature -than the one obtained from a bias sweep at the same refrigerator temperature (dark blue trace), see also SOM 34 . Therefore, the CBT is used in secondary mode here for the rest of this work 18,29,30 . The normalized Coulomb blockade zero bias dip δg = 1 − g 0 /g T is given by the third order expansion…”

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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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“…Due to Coulomb blockade effects 36 , the zero bias conductance g 0 is suppressed below its asymptotic, large bias value g T . Both width and depth of the conductance dip are commonly used for thermometry 18,29 . While fitting the full conductance trace allows one to use the CBT as a primary thermometer, using the depth of the zero bias dip requires pre- calibration and thus can be used only as a secondary thermometer.…”

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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 SI Kelvin and the Boltzmann Constant

2019

The New International System of Units (SI)

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Metallic Coulomb blockade thermometry down to 10 mK and below

Cited by 33 publications

References 18 publications

Intrinsic Metastabilities in the Charge Configuration of a Double Quantum Dot

Intrinsic Metastabilities in the Charge Configuration of a Double Quantum Dot

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

The SI Kelvin and the Boltzmann Constant

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