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Conference on Lasers and Electro-Optics Europe & European Quantum Electronics Conference (CLEO/Europe-EQEC)

Two-photon blockade in quantum electrodynamics

Karl Nicolas Tolazzi, Christoph Hamsen, Tatjana Wilk, Gerhard Rempe

Published Jun 1, 2017• 0 citations
Publisher

Abstract

Summary form only given. Open driven quantum systems exhibit fluctuations during their walk through Hilbert space. These can be reduced by blocking parts of the Hilbert space. For discrete variables such as particle number a blockade can result from a sufficiently strong interaction between the involved quanta, for example, the effective interaction of photons in an optically nonlinear medium.We implemented the blockade in a strongly coupled cavity quantum electrodynamics system consisting of a single two-level atom strongly coupled to a high finesse optical resonator (see Fig. 1a). This combined system exhibits a new energy structure with an anharmonic ladder of dressed states that scales with ,/n (see Fig. 1b), where n is the number of excitations. Only this special structure provides a photon-number dependent nonlinearity which is necessary to address specific manifolds with the drive.

DOI
10.1109/cleoe-eqec.2017.8087324

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Summary form only given. Open driven quantum systems exhibit fluctuations during their walk through Hilbert space. These can be reduced by blocking parts of the Hilbert space. For discrete variables such as particle number a blockade can result from a sufficiently strong interaction between the involved quanta, for example, the effective interaction of photons in an optically nonlinear medium.We implemented the blockade in a strongly coupled cavity quantum electrodynamics system consisting of a single two-level atom strongly coupled to a high finesse optical resonator (see Fig. 1a). This combined system exhibits a new energy structure with an anharmonic ladder of dressed states that scales with ,/n (see Fig. 1b), where n is the number of excitations. Only this special structure provides a photon-number dependent nonlinearity which is necessary to address specific manifolds with the drive.
Photon blockade is a dynamical quantum-nonlinear effect in driven systems with an anharmonic energy ladder. For a single atom strongly coupled to an optical cavity, we show that atom driving gives a decisively larger optical nonlinearity than cavity driving. This enhances single-photon blockade and allows for the implementation of two-photon blockade where the absorption of two photons suppresses the absorption of further photons. As a signature, we report on three-photon antibunching with simultaneous two-photon bunching observed in the light emitted from the cavity. Our experiment constitutes a significant step towards multiphoton quantum-nonlinear optics.
Photon blockade, in analogy to Coulomb's or phonon blockades, is a phenomenon when a single photon in a nonlinear cavity blocks the transmission of a second photon. This effect can occur in Kerr-type systems driven by a laser due to strong nonlinear photon-photon interactions. We predict the occurrence of higher-order photon blockades where the transmission of more than two photons is effectively blocked by single- and two-photon states. This photon blockade can be achieved by tuning the frequency of the laser driving field to be equal to the sum of the Kerr nonlinearity and the cavity resonance frequency. We refer to this phenomenon as two-photon blockade or two-photon state truncation via nonlinear scissors, and can also be interpreted as photon-induced tunneling. We also show that, for a driving-field frequency fulfilling another resonance condition and for higher strengths of the driving field, even a three-photon blockade can occur but less clearly than in the case of single- and two-photon blockades. We demonstrate how various photon blockades can be identified by analyzing photon-number correlations, coherence and entropic properties, Wigner functions, and spectra of squeezing. We show that two- and three-photon blockades can, in principle, be observed in various cavity and circuit quantum electrodynamical systems for which the standard single-photon blockade was observed without the need of using higher-order driving interactions or Kerr media exhibiting higher-order nonlinear susceptibility.
We present a study of collective multiphoton blockade in coherently driven atoms in a single-mode cavity. Considering two atoms strongly coupled to an optical cavity, we show that the two-photon blockade with two-photon antibunching, and the three-photon blockade with three-photon antibunching can be observed simultaneously. The three-photon blockade probes both dressed states in the two-photon and three-photon spaces. The two-photon and three-photon blockades strongly depend on the location of the two atoms in the strong-coupling regime. The asymmetry in the atom-cavity coupling constants opens pathways for multiphoton blockade which is also shown to be sensitive to the atomic decay and pumping strengths. The work presented here predicts many quantum statistical features due to the collective behavior of atoms and can be useful to generate nonclassical photon pairs.
We investigate theoretically the model of a cavity-quantum-electrodynamics (QED) system that consists of two two-level atoms coupled to a single-mode cavity in the weak coupling regime, where the system is driven by quantum light. The dynamics behavior of the entire system is tackled in the framework of a cascaded quantum system. We find that the two-photon blockade with two-photon bunching and three-photon antibunching can be obtained even when the strong system dissipation is included. This result shows that our work has potential for realizing entangled photon pairs in a weakly coupled cavity. Moreover, we also analyze the photon statistics of the system in the case of out-of-resonance coupling between cavity and two nonidentical atoms. Here, an unconventional photon blockade effect with suppression of two-photon correlation and enhancement of three-photon correlation can be realized, which shows many quantum statistical characteristics of a cavity QED system in weak coupling.
Analogous to Coulomb blockade for electrons, photon blockade is a key quantum optical effect in which the presence of one photon prevents the transmission of subsequent ones through a nonlinear medium. Beyond its fundamental interest, photon and multi-photon blockade are actively studied as mechanisms for generating technologically-relevant quantum states of light. Although photon blockade typically requires achieving strong light-matter coupling, increasing the number of atoms fails to enhance antibunching. Here, we analyze the optical transmission properties of a quantum resonator that embeds a two-photon-coupled ensemble of emitters, combining an approximate analytical approach with full quantum numerical simulations. We show that when light and matter are coupled via a two-photon interaction, both single- and multi-photon blockade can benefit from a collective enhancement. We propose different driving schemes in which the second or third-order correlation functions are strongly suppressed with increasing atom number. Differently from established methods, this collective enhancement of non-classical properties occurs with unitary transmission and is ultimately constrained only by decoherence. This demonstrates that collective two-photon couplings are a powerful mechanism for realizing photon blockade even in platforms where individual strong coupling is not achievable.
Atoms absorb and emit resonant light photon by photon. However, an atom strongly coupled to the light field of a high-finesse optical resonator forms a new system with new characteristics, enabling the emission and absorption of photon pairs. The energy eigenstates of the coupled system form an anharmonic ladder of doublets, the so-called Jaynes-Cummings ladder. The first doublet, consisting of the two so-called normal modes, has been observed in various cavity QED systems. It can be explained classically using Maxwell equations as arising from the coupling of a classical dipole to a classical electromagnetic field. In contrast, the higher-order doublet has so far no classical analogue. It requires both the quantization of the atomic internal state as well as the quantization of light.