Detection and amplification of spin noise using scattered laser light in a quantum-dot microcavity

Abstract

Fundamental properties of the spin-noise signal formation in a quantum-dot microcavity are studied by measuring the angular characteristics of the scattered light intensity. A distributed Bragg reflector microcavity was used to enhance the light-matter interaction with an ensemble of n-doped (In,Ga)As/GaAs quantum dots, which allowed us to study subtle effects of the noisesignal formation. Detecting the scattered light outside of the aperture of the transmitted light, we measured the basic electron spin properties, like g-factor and spin dephasing time. Further, we investigated the influence of the microcavity on the scattering distribution and possibilities of signal amplification by additional resonant excitation.In recent years optical spin noise spectroscopy (SNS) has developed into an efficient research tool in the field of spin physics [1,2]. Initially demonstrated in thermal vapors of alkali atoms [3,4], it has been further applied to spins in bulk and low-dimensional semiconductor structures [5][6][7][8][9], and recently extended to studies of the valley dynamics in monolayer semiconductors [10] and the magnetization fluctuations in ultrathin metal films [11].In optical SNS, the fluctuations of the magnetization close to the ground state are mapped onto Faraday rotation angle fluctuations using magneto-optical effects [12]. In other terms, the spin noise signal arises from an interference of the forward-scattered field with the transmitted driving laser [13][14][15]. Therefore, understanding of the scattering gives a direct link to the properties of the studied system [16].In general, the measured spin noise signal is proportional to the probe beam intensity squared. Thus, increasing intensity, on the one hand, improves the sensitivity of the measurements but, on the other hand, increases unwanted perturbations of the system [17,18]. One possibility to decrease these perturbations could be the use of optical resonators, in particular, microcavities, which can be considered as an efficient tool of signal amplification [9,19,20]. This possibility is, however, not optimal, as the increased light-matter interaction leads to an increased perturbation of the system, so that a strong reduction of the light intensity is required. Furthermore, additional limitations are given by the diode detectors, which limit the sensitivity of the recorded signal at low level optical intensities by their own electrical noise. A solution could be provided by the basic properties of the spin noise signal formation, i.e. by the fact that a coherent superposition of the driving laser field with the forward-scattered field is equivalent to implementing a homodyne detection. In this case, the laser transmitted through the sample can be replaced by a part of the laser beam, which is not going through the sample and therefore does not interact with the system. This allows one to use a very low probe power for accessing the spin noise while working with high power laser light hitting the diodes [21][22][23].In this paper, we examine the...

Extending the time of coherent optical response in ensemble of singly-charged InGaAs quantum dots

“…They are determined by the Larmor precession frequencies ω e and ω h , delay time τ 12 , trion lifetime τ r . The g-factors of electrons and holes are known from previous studies [32,33]. Therefore, the only unknown parameter is the spin dephasing time of resident electrons T * 2,e .…”

Extending the time of coherent optical response in ensemble of singly-charged InGaAs quantum dots

“…They are determined by the Larmor precession frequencies ω e and ω h , delay time τ 12 , trion lifetime τ r . The gfactors of electrons and holes are known from previous studies 30,33 . Therefore, the only unknown parameter is the spin dephasing time of resident electrons T Ã 2;e .…”

Raman scattering model of the spin noise

“…The fact that magnetization noise is observed in SNS as the polarization noise of the probe laser light and is caused by fluctuations of the optical susceptibility of the sample shows a similarity of the SNS and Raman spectroscopy. Thus, due to combination of the features of the EPR and Raman spectroscopy, the SNS reveals a number of unique features related to nonperturbativity of the SNS [35,36], to possibility of tuning the frequency of the probe laser light [37,38] and its spatial localization [39], to possibility of using multi-beam configurations [40,41] and some others.…”