Observation of the Unconventional Photon Blockade

Abstract

We observe the unconventional photon blockade effect in quantum dot cavity QED, which, in contrast to the conventional photon blockade, operates in the weak coupling regime. A single quantum dot transition is simultaneously coupled to two orthogonally polarized optical cavity modes, and by careful tuning of the input and output state of polarization, the unconventional photon blockade effect is observed. We find a minimum second-order correlation g ð2Þ ð0Þ ≈ 0.37, which corresponds to g ð2Þ ð0Þ ≈ 0.005 when corrected for detector jitter, and observe the expected polarization dependency and photon bunching and antibunching; close by in parameter space, which indicates the abrupt change from phase to amplitude squeezing. DOI: 10.1103/PhysRevLett.121.043601 A two-level system strongly coupled to a cavity results in polaritonic dressed states with a photon-number dependent energy. This dressing gives rise to the photon blockade effect [1,2] resulting in photon-number dependent transmission and reflection, enabling the transformation of incident coherent light into specific photon number states such as single photons. Single photon sources are a crucial ingredient for various photonic quantum technologies ranging from quantum key distribution to optical quantum computing. Such sources are characterized by a vanishing second-order autocorrelation g ð2Þ ð0Þ ≈ 0 [3]. In the strong coupling regime, where the coupling between the two-level system and the cavity is larger than the cavity decay rate ðg > κÞ [4], photon blockade has been demonstrated in atomic systems [5], quantum dots in photonic crystal cavities [6], and circuit QED [7,8]. At the onset of the weak coupling regime (g ≈ κ), it has been shown that by detuning the dipole transition frequency with respect to the cavity resonance, photon blockade can still be observed [9]. However, moving further into the weak coupling regime (g < κ), which is much easier to achieve [10,11] (in particular if one aims for a small polarization mode splitting), the conventional photon blockade is no longer possible because the energy gap between the polariton states vanishes. Nevertheless, also in the weak coupling regime, the two-level system enables photon number sensitivity, which has recently enabled high-quality single photon sources using polarization postselection [12][13][14] or optimized cavity in-coupling [15,16].In 2010, Liew and Savona introduced the concept of the unconventional photon blockade (UPB) [17,18]

Strong Photon Blockade Mediated by Optical Stark Shift in a Single-Atom–Cavity System

“…This mechanism relying on strong energy-spectrum anharmonicity, * dengyg3@mail.sysu.edu.cn † lichaoh2@mail.sysu.edu.cn is referred to as conventional PB, and remains a great challenge, despite some experimental advances in realizing strong coupling in a high-finesse cavity [36][37][38][39][40][41][42][43][44]. In contrast to conventional PB, unconventional PB has led to tremendous advances in achieving strong antibunching of photons by using quantum interference [45][46][47][48][49][50][51][52][53], in which the basic principle is based on constructive interference between different quantum transition paths from the ground state to a two-photon excitation state. Unconventional PB has been observed experimentally in systems ranging from a single-quantum-dot cavity [52] to, currently, two coupled superconducting resonators [53].…”

“…In contrast to conventional PB, unconventional PB has led to tremendous advances in achieving strong antibunching of photons by using quantum interference [45][46][47][48][49][50][51][52][53], in which the basic principle is based on constructive interference between different quantum transition paths from the ground state to a two-photon excitation state. Unconventional PB has been observed experimentally in systems ranging from a single-quantum-dot cavity [52] to, currently, two coupled superconducting resonators [53]. However, the quantum interference mechanism cannot eliminate all multiphoton excitations simultaneously, even if the two-photon excitation state is suppressed completely.…”

Dynamical Blockade in a Single-Mode Bosonic System

“…In the required strong coupling regime, this correlation function rapidly oscillates in time. Observing the unconventional blockade thus requires high time resolution [33,34]. In our dynamical blockade, the timescale controlling g 2 (t, t s ) is given by the photon life time /γ, that is, a natural time resolution in emission from the mode.…”

“…Alternatively, an interference effect between a pair of coupled quantum modes can induce unconventional photon blockade in the weakly nonlinear regime [28][29][30][31][32], which was realized in recent experiments [33,34]. However, the emission-correlation in the unconventional blockade rapidly oscillates in time [28], requiring high time resolution to observe, as well as making it unsuitable for many applications.…”

Generation of Non‐Classical Light Using Semiconductor Quantum Dots

“…Oxide aperture cavities are a lot like micropillar resonators with the difference that the pillar has a larger diameter of m . However, the mode is confined to a diameter similar to micropillars using an oxide aperture above the QD layer resulting in comparable Purcell factors .…”