Efficiency vs multi-photon contribution test for quantum dots

Abstract

The development of linear quantum computing within integrated circuits demands high quality semiconductor single photon sources. In particular, for a reliable single photon source it is not sufficient to have a low multi-photon component, but also to possess high efficiency. We investigate the photon statistics of the emission from a single quantum dot with a method that is able to sensitively detect the trade-off between the efficiency and the multi-photon contribution. Our measurements show, that the light emitted from the quantum dot when it is resonantly excited possess a very low multi-photon content. Additionally, we demonstrated, for the first time, the non-Gaussian nature of the quantum state emitted from a single quantum dot.The ideal single photon state is quantum mechanically represented by the Fock state |1 , a quantum counterpart of the classical particle. The particle nature of a single photon is traditionally verified by observing an anticorrelation effect on a beam splitter [1]. This measurement of the intensity autocorrelation is commonly accepted as the way to test a light source for non-classicality [2]. Nonetheless, such a measurement is an intensitynormalized measurement and therefore completely insensitive to the vacuum contribution, |0 . In practice, however, all single-photon sources emit a stochastic mixture of the vacuum and the Fock state |1 . For many applications, which do not depend on the efficiency of the singlephoton source the intensity autocorrelation is a sufficient test. On the other hand, applications like linear optical quantum computing [3] crucially depend on the overall source and detector efficiency [4][5][6].Seen from this perspective, the characterization of a quantum state produced by realistic single photon sources would strongly benefit from a measurement that is sensitive to the vacuum contribution as well as the multiphoton component. By measuring the density matrix one obtains the full information about the quantum state of a real single photon source; regrettably, such a full state tomography is usually quite challenging. An alternative approach is to measure a quantum phase-space description of the state, its so-called Wigner function [7]. It is well known that the single photon state |1 has a negative Wigner function [8,9]. Furthermore, there is a whole class of states that possess negative Wigner functions (so called non-Gaussian states of light) as shown by Hudson's theorem [10]. The Wigner function is usually measured by homodyne tomography. This is a very tedious procedure and in some cases even impossible. However, when it is possible, it can detect the negativity of the states Wigner function, as was demonstrated for heralded single photon sources [11]. The practical obstacle for such a measurement is that the negativity depends crucially on the overall source and detector efficiency η. Namely, if η < 0.5 the measured Wigner function is positive, even though the photon source may give a perfectly antibunched intensity autocorrelation measurement. Theref...

Detecting quantum non-Gaussianity via the Wigner function

“…An experimentally friendly criterion for quantum nonGaussianity, based on photon number probabilities, has been introduced [26], and then employed in different experimental settings to prove the generation of quantum non-Gaussian states, such as heralded single-photon states [27], squeezed single-photon states [28] and Fock states from a semiconductor quantum dot [29].…”

Hyperentanglement of photons emitted by a quantum dot

“…These achievements combined with the possibility of photon storage [6] show the potential of quantum dots to become building blocks of a quantum network [7]. Due to their discrete energy level structure quantum dots are inherently antibunched single photon [8] sources with sub-Poissonian statistics [9] which allows them to produce very pure single photon states [1,2].The application of entanglement of photons includes quantum communications [10,11], where it can be used as resource in information exchange protocols like teleportation [12] and entanglement swapping [13]. In addition, entanglement is an essential element of linear optical quantum computing [14].…”

“…These achievements combined with the possibility of photon storage [6] show the potential of quantum dots to become building blocks of a quantum network [7]. Due to their discrete energy level structure quantum dots are inherently antibunched single photon [8] sources with sub-Poissonian statistics [9] which allows them to produce very pure single photon states [1,2].…”

Coherence and degree of time-bin entanglement from quantum dots

“…This results in a high degree of entanglement with a concurrence of up to 0.78(6) and a 0.88(3) overlap with a maximally entangled state. Theoretical simulations also indicate a power dependent nature of the dephasing during the laser excitation that limits the coherence of the excitation process.Single semiconductor quantum dots, due to their discrete energy structure, constitute an antibunched single photon source at a well defined frequency and with inherently sub-Poissonian statistics [1]. They generate single photons through a recombination of an exciton, a quasi particle formed by a Coulomb-bound electron from the conduction band and a hole from the valence band.…”

“…Single semiconductor quantum dots, due to their discrete energy structure, constitute an antibunched single photon source at a well defined frequency and with inherently sub-Poissonian statistics [1]. They generate single photons through a recombination of an exciton, a quasi particle formed by a Coulomb-bound electron from the conduction band and a hole from the valence band.…”