We probe the indistinguishability of photons emitted by a semiconductor quantum dot (QD) via time- and temperature-dependent two-photon interference (TPI) experiments. An increase in temporal separation between consecutive photon emission events reveals a decrease in TPI visibility on a nanosecond time scale, theoretically described by a non-Markovian noise process in agreement with fluctuating charge traps in the QD's vicinity. Phonon-induced pure dephasing results in a decrease in TPI visibility from (96±4)% at 10 K to a vanishing visibility at 40 K. In contrast to Michelson-type measurements, our experiments provide direct access to the time-dependent coherence of a quantum emitter on a nanosecond time scale.

Two‐dimensional layers of transition metal dichalcogenides (TMDCs) represent semiconductors with a complex single‐particle bandstructure and reduce screening of the three‐dimensional Coulomb interaction. The efficient Coulomb interaction causes optical excitations close to the band edge to be dominated by strongly correlated, bound electron–hole pairs, called excitons. Here, a theoretical formalism is presented to efficiently describe the optical dynamics of atomically thin TMDCs in a naturally adapted two particle exciton basis. As an example, Coulomb intravalley coupling, intervalley exchange, as well as intrinsic and Dexter‐like intervalley interactions are discussed in Hartree–Fock approximation.

We present a microscopically based scheme for the generation of coherent cavity phonons (phonon laser) by an optically driven semiconductor quantum dot coupled to a THz acoustic nanocavity. External laser pump light on an anti-Stokes resonance creates an effective Lambda system within a two-level dot that leads to coherent phonon statistics. We use an inductive equation of motion method to estimate a realistic parameter range for an experimental realization of such phonon lasers. This scheme for the creation of nonequilibrium phonons is robust with respect to radiative and phononic damping and only requires optical Rabi frequencies of the order of the electron-phonon coupling strength.

We propose a scheme to control cavity quantum electrodynamics in the single photon limit by delayed feedback. In our approach a single emitter-cavity system, operating in the weak coupling limit, can be driven into the strong coupling-type regime by an external mirror: The external loop produces Rabi oscillations directly connected to the electron-photon coupling strength. As an expansion of typical cavity quantum electrodynamics, we treat the quantum correlation of external and internal light modes dynamically and demonstrate a possible way to implement a fully quantum mechanical time-delayed feedback. Our theoretical approach proposes a way to experimentally feedback control quantum correlations in the single photon limit.

In quantum optics the g (2) -function is a standard tool to investigate photon emission statistics. We define a g (2) -function for electronic transport and use it to investigate the bunching and antibunching of electron currents. Importantly, we show that super-Poissonian electron statistics do not necessarily imply electron bunching, and that sub-Poissonian statistics do not imply anti-bunching. We discuss the information contained in g (2) (τ ) for several typical examples of transport through nano-structures such as few-level quantum dots.PACS numbers: 73.63. Kv, 73.50.Td, 73.23.Hk Current noise has long-since been established as an important tool for studying the physics of transport through mesoscopic and nano-scale conductors 1-5 . The character of the noise is typically assessed by considering the Fano factor, the ratio of the zero-frequency noise to the current 3 , and comparing with a Poisson process for which the Fano factor is equal to one. Systems with F < 1 are described as sub-Poissonian (non-interacting systems fall in this class 2 ) and systems which have F > 1 are called super-Poissonian. A common interpretation of this comparison is that a super-Poissonian Fano factor indicates a bunching of the current's constituent electrons, whereas sub-Poissonian values indicates anti-bunching (Fig. 1 ).In this paper we directly investigate bunching and antibunching in electronic transport as a phenomenon in the time domain through the introduction of a second-order correlation function g (2) (τ ), analogous to that used in quantum optics [6][7][8] . Within a quantum master equation (QME) framework in the appropriate limit, the g (2) -function is seen to be proportional to the conditional probability that, given an electron is emitted into the collector at time t = 0, a further such jump is observed a time τ later. Following quantum optics, we identifysince bunching means that particles are more likely to be emitted together than apart, and conversely for antibunching. By relating our g (2) -function to the correlation function between the current at two different times, we clarify the relationship between the g (2) -function, (anti-) bunching and the Fano factor.We then investigate bunching and anti-bunching in several widely-discussed transport models in the Coulomb blockade (CB) regime (see Fig. 2). This analysis shows that the simple picture relating superPoissonian Fano factors to bunching and sub-Poissonian ones to anti-bunching is often an oversimplification, and can even be outright wrong. In particular we discuss a simple quantum-dot (QD) model which has a Fano factor less than one, and is thus sub-Poissonian, and yet has g (2) (0) > g (2) (τ ) for all τ > 0 such that, according to Eq. (1), the electron-flow is completely bunched. We also give a model for which the converse is true, i.e. we find a super-Poissonian Fano factor in conjunction with electron anti-bunching. These results mirror the work of Singh 9 and Zou and Mandel 10 , who have made similar points for quantum-optical systems.This ...

A non-classical light source emitting pairs of identical photons represents a versatile resource of interdisciplinary importance with applications in quantum optics and quantum biology. To date, photon twins have mostly been generated using parametric downconversion sources, relying on Poissonian number distributions, or atoms, exhibiting low emission rates. Here we propose and experimentally demonstrate the efficient, triggered generation of photon twins using the energy-degenerate biexciton–exciton radiative cascade of a single semiconductor quantum dot. Deterministically integrated within a microlens, this nanostructure emits highly correlated photon pairs, degenerate in energy and polarization, at a rate of up to (234±4) kHz. Furthermore, we verify a significant degree of photon indistinguishability and directly observe twin-photon emission by employing photon-number-resolving detectors, which enables the reconstruction of the emitted photon number distribution. Our work represents an important step towards the realization of efficient sources of twin-photon states on a fully scalable technology platform.

We investigate the resilience of symmetry-protected topological edge states at the boundaries of Kitaev chains in the presence of a bath which explicitly introduces symmetry-breaking terms. Specifically, we focus on single-particle losses and gains, violating the protecting parity symmetry, which could generically occur in realistic scenarios. For homogeneous systems, we show that the Majorana mode decays exponentially fast. By the inclusion of strong disorder, where the closed system enters a many-body localized phase, we find that the Majorana mode can be stabilized substantially. The decay of the Majorana converts into a stretched exponential form for particle losses or gains occuring in the bulk. In particular, for pure loss dynamics we find a universal exponent α 2/3. We show that this holds both in the Anderson and many-body localized regimes. Our results thus provide a first step to stabilize edge states even in the presence of symmetry-breaking environments.

The Jaynes-Cummings model provides a well established theoretical framework for single electron two level systems in a radiation field. Similar exactly solvable models for semiconductor light emitters such as quantum dots dominated by many particle interactions are not known. We access these systems by a generalized cluster expansion, the photon-probability cluster expansion: a reliable approach for few-photon dynamics in many body electron systems. As a first application, we discuss vacuum Rabi oscillations and show that their amplitude determines the number of electrons in the quantum dot.