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An in situ tunable radio-frequency quantum point contact
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View: Figures


Image of FIG. 1.
FIG. 1.

(a) Experimental setup used for time-resolved measurements. The variable capacitance diode in series to the circuit allows for in situ tunability. The quantum point contact, defined by atomic force microscopy lithography, is sensitive to charges in the nearby double quantum dot. (b) Tuning of the resonance frequency by applying voltages in steps of 0.5 V to the variable capacitance diode at fixed QPC conductance of . (c) Change in reflection for different QPC conductance values at diode voltages of 0, 1, 2.7, and 5 V (ascending resonant frequencies).

Image of FIG. 2.
FIG. 2.

(a) Simultaneous time traces, eighth order software filtered at 50 kHz. The feedback resistor of the dc current-voltage converter was . (b) Histograms of the time traces taken in (a). [(c) and (d)] Spectral densities of the dc and rf time traces as shown in (a), lowpass filtered at 100 kHz instead of 50 kHz. The solid green line in (d) represents the expected amplifier noise level at .

Image of FIG. 3.
FIG. 3.

Comparison between performance of rf reflection (empty blue squares) and conventional dc (filled red dots) techniques. Signal to noise ratios (SNR) are given in logarithmic power scale. With the exception of the bandwidth dependent data in (d), all raw data has been eighth order lowpass filtered at 1 kHz by software prior to analysis. (a) rf and dc SNR as a function of QPC conductance at fixed diode voltage of 2.7 V. The rf input power was set to −80 dBm, the dc bias to . (b) Influence of incident rf power on dc and rf SNR at constant dc bias of and optimal QPC conductance of . (c) SNR for different diode voltages at optimal QPC values . (d) Using all previously determined optimal values, the frequency of the software lowpass filter is changed to estimate the limits of both techniques. The dashed line shows the expected linear decay of the SNR with bandwidth.


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Scitation: An in situ tunable radio-frequency quantum point contact