Using a Quantum Dot as a High-Frequency Shot Noise Detector

Abstract

We present the experimental realization of a quantum dot (QD) operating as a high-frequency noise detector. Current fluctuations produced in a nearby quantum point contact (QPC) ionize the QD and induce transport through excited states. The resulting transient current through the QD represents our detector signal. We investigate its dependence on the QPC transmission and voltage bias. We observe and explain a quantum threshold feature and a saturation in the detector signal. This experimental and theoretical study is relevant in understanding the backaction of a QPC used as a charge detector. DOI: 10.1103/PhysRevLett.96.176601 PACS numbers: 72.70.+m, 73.21.La, 73.23.ÿb On chip noise detection schemes, where device and detector are capacitively coupled within submillimeter length scales, can benefit from large frequency bandwidths. This results in a good sensitivity and allows one to study the quantum limit of noise, where an asymmetry can occur in the spectrum between positive and negative frequencies. The asymmetry, caused by the difference in the occurrence probability of emission and absorption processes, can be probed using quantum detectors [1]. In this Letter, we investigate the transport through a quantum dot (QD) under the influence of high-frequency irradiation generated by a nearby quantum point contact (QPC). The QPC current fluctuations induce photoionization, taking the QD out of Coulomb blockade, thereby allowing sequential tunneling through an excited state [2,3]. By studying this transient current while changing the QPC parameters, we show that we can perform high-frequency shot noise detection in the 20 -250 GHz frequency range.The granularity of the electrons and the stochastic nature of their transport lead to unavoidable temporal fluctuations in the electrical current, i.e., shot noise [4]. For systems where transport is completely uncorrelated, such as vacuum diodes [5], noise is characterized by a Poissonian value of the power spectral density S I 2eI dc . Here we use the QPC as a well-known noise source. When the QPC is driven out of equilibrium, i.e., by applying an electrochemical potential difference between the source and the drain of the QPC, a net current will flow if the QPC is not pinched off. At zero temperature (k B T eV QPC ), the stream of incident electrons is noiseless, and shot noise, due to particle partition, dominates. The electrons are either transmitted or reflected, with a probability depending on the QPC transmission T. The power density can be written as S I 2eI dc F, where F P N i 0 T i 1 ÿ T i = P N i 0 T i is the Fano factor and the summation is over transport channels with transmissions T i . In this case, correlations in the transport are introduced by the Pauli exclusion principle, resulting in a suppression of noise below the Poissonian value. Thus, shot noise vanishes if all the 1D quantum channels either fully transmit (In many recent experiments, QPCs are used as charge detectors [7]. In this context, our experiment provides information regarding the ba...

Coulomb drag

“…Interactively coupled mesoscopic and nanoscale circuits, such as quantum wires (Debray et al, 2000(Debray et al, , 2001Laroche et al, 2011;Morimoto et al, 2003;Yamamoto et al, 2006), quantum dots (Aguado and Kouwenhoven, 2000;Onac et al, 2006) or point contacts (Khrapai et al, 2006(Khrapai et al, , 2007, provided new fruitful ways of studying Coulomb drag phenomena and revealed a plethora of interesting physics. These devices typically have dimensions smaller than the temperature length L T = v F /T and voltage-related length scale L V = v F /(eV ), and differ substantially from their two-dimensional quantumwell counterparts in several important ways.…”

“…Twolevel pulse technique was used to detect individual electron spin (Elzerman et al, 2004). Quantum dots were also used as high-frequency noise detectors (Onac et al, 2006). Transport measurements on adjacent but electrically isolated quantum point contacts (QPCs) exhibit a counterflow of electrons [i.e.…”

Transient current-current correlations and noise spectra

“…As one see, the transient current-current correlations have been expressed explicitly in terms of our nonequilibrium Green's functions u(t, t 0 ) and v(τ, t) that determine the dissipation and fluctuation coefficients in the exact master equation (10).…”

“…[16][17][18][19] The asymmetric noise spectrum, which is directly proportional to the emission-absorption spectrum of the system, 20 has been demonstrated experimentally. [9][10][11][12] In recent years, the higher order current-correlations in a nonequilibrium steady state are also explored both in experimental and theoretical studies. 21,22 The above investigations were focused on the steadystate transport regime.…”

“…6 Conventionally, evaluations of noise spectra are largely limited to the rather low frequency ( ω ≪ k B T ), where the noise spectrum is symmetric at zero bias. 7 However, experimental measurements of high frequency noise spectra [8][9][10][11] inspired the exploration of the frequency-resolved noise spectrum both in symmetric [13][14][15] and asymmetric form. [16][17][18][19] The asymmetric noise spectrum, which is directly proportional to the emission-absorption spectrum of the system, 20 has been demonstrated experimentally.…”