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Interacting Photons in a Strongly Coupled Atom-Cavity System

Christoph Hamsen

Published Jan 1, 2017• 1 citation
OpenAlex

Abstract

Optical photons do not interact in vacuum. Therefore, we employ a single atom strongly coupled to a cavity to mediate interactions between photons, first, within a single light field and, second, in two different light fields. For the former, we demonstrate a two-photon blockade whereby the absorption of two photons blocks further excitation. For the latter, we realize strong nonlinear coupling between photons in different cavity modes which can either mutually block each other or only transit the system conjunctly.

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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.

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A two-level system interacting with a cavity field is an important model for investigating the photon blockade (PB) effect. Most work on this topic has been based on the assumption that the atomic transition frequency is resonant with the fundamental mode frequency of the cavity. We relax this constraint and reexamine PB in a more general atom--cavity system with arbitrary atomic and cavity detunings from a driving field. The results show that when the signs of the atomic and cavity detunings are the same, PB occurs only in the strong-coupling regime, but for opposite signs of the atomic and cavity detunings, strong photon antibunching is observed in both the weak- and strong-coupling regimes and a better PB effect is achieved compared with the case when the signs are the same. More interestingly, we find that this PB arises from quantum interference for both weak and strong nonlinearities. These results deepen our understanding of the underlying mechanism of PB and may be help in the construction of single-photon sources with higher purity and better flexibility using atom--cavity systems.

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Photon Blockade with Memory and Slow Light using a Single Atom in an Optical Cavity

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The realization of nonlinear systems able to mediate strong interactions between light fields at the few photon level in an environment with minimal absorption represents a cornerstone for future developments of quantum information science and photonic quantum technologies.One approach to reach this goal is via strong coupling of single emitters to optical cavities as provided by cavity quantum electrodynamics (QED).The other one is via electromagnetically induced transparency (EIT) with single atoms or with atomic ensembles.This thesis reports on a system which merges both single-atom cavity QED in the strong coupling regime and EIT.First, we characterize this system theoretically and show that its energy eigenstates are very similar to the well known Jaynes-Cummings ladder of eigenstates.However, here, the eigenstates are optically controllable via the control field Rabi frequency provided by EIT.We show that increasing the control field Rabi frequency enhances the normalmode splitting, and therefore the effective light-matter coupling.Moreover, with this system we are able to observe photon blockade and a two-photon gateway for the same input probe field and to tune the behavior of the secondorder correlation function optically.Thanks to the long coherence times of EIT, photon blockade can be prolonged in time for longer times than the decay rates of the system.We refer to this effect as photon blockade with memory.Next, we verify our theoretical findings experimentally.By performing spectroscopy measurements on the single-atom cavity EIT system, we show an unprecedented EIT on/off contrast of about 80 % thanks to our strong atomcavity coupling rate.Later, we show experimentally, the ability to generate both, photon blockade and a two-photon gateway, for the same input field by just varying the control field Rabi frequency.Finally, by performing timedependent second-order correlations we observe strong oscillations in the correlations which are a result of the creation of a new light field in the cavity which beats with the impinging probe laser.We show experimentally that this new field has a coherence time longer than the decay rates of the system, confirming its EIT origin.In a final experiment, we take advantage of the strong atom-cavity coupling achieved to induce a group delay on probing pulses.Delays up to approximately 200 ns are measured.This is the first time a group delay is observed with a single atom as the delaying medium.iii

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Two-photon blockade in quantum electrodynamics

Karl Nicolas Tolazzi, Christoph Hamsen, Tatjana Wilk +1 more

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.

Conference on Lasers and Electro-Optics Europe & European Quantum Electronics Conference (CLEO/Europe-EQEC)•Jun 1, 2017•0 citations
Optical photons do not interact in vacuum. Therefore, we employ a single atom strongly coupled to a cavity to mediate interactions between photons, first, within a single light field and, second, in two different light fields. For the former, we demonstrate a two-photon blockade whereby the absorption of two photons blocks further excitation. For the latter, we realize strong nonlinear coupling between photons in different cavity modes which can either mutually block each other or only transit the system conjunctly.
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.
A two-level system interacting with a cavity field is an important model for investigating the photon blockade (PB) effect. Most work on this topic has been based on the assumption that the atomic transition frequency is resonant with the fundamental mode frequency of the cavity. We relax this constraint and reexamine PB in a more general atom--cavity system with arbitrary atomic and cavity detunings from a driving field. The results show that when the signs of the atomic and cavity detunings are the same, PB occurs only in the strong-coupling regime, but for opposite signs of the atomic and cavity detunings, strong photon antibunching is observed in both the weak- and strong-coupling regimes and a better PB effect is achieved compared with the case when the signs are the same. More interestingly, we find that this PB arises from quantum interference for both weak and strong nonlinearities. These results deepen our understanding of the underlying mechanism of PB and may be help in the construction of single-photon sources with higher purity and better flexibility using atom--cavity systems.
The realization of nonlinear systems able to mediate strong interactions between light fields at the few photon level in an environment with minimal absorption represents a cornerstone for future developments of quantum information science and photonic quantum technologies.One approach to reach this goal is via strong coupling of single emitters to optical cavities as provided by cavity quantum electrodynamics (QED).The other one is via electromagnetically induced transparency (EIT) with single atoms or with atomic ensembles.This thesis reports on a system which merges both single-atom cavity QED in the strong coupling regime and EIT.First, we characterize this system theoretically and show that its energy eigenstates are very similar to the well known Jaynes-Cummings ladder of eigenstates.However, here, the eigenstates are optically controllable via the control field Rabi frequency provided by EIT.We show that increasing the control field Rabi frequency enhances the normalmode splitting, and therefore the effective light-matter coupling.Moreover, with this system we are able to observe photon blockade and a two-photon gateway for the same input probe field and to tune the behavior of the secondorder correlation function optically.Thanks to the long coherence times of EIT, photon blockade can be prolonged in time for longer times than the decay rates of the system.We refer to this effect as photon blockade with memory.Next, we verify our theoretical findings experimentally.By performing spectroscopy measurements on the single-atom cavity EIT system, we show an unprecedented EIT on/off contrast of about 80 % thanks to our strong atomcavity coupling rate.Later, we show experimentally, the ability to generate both, photon blockade and a two-photon gateway, for the same input field by just varying the control field Rabi frequency.Finally, by performing timedependent second-order correlations we observe strong oscillations in the correlations which are a result of the creation of a new light field in the cavity which beats with the impinging probe laser.We show experimentally that this new field has a coherence time longer than the decay rates of the system, confirming its EIT origin.In a final experiment, we take advantage of the strong atom-cavity coupling achieved to induce a group delay on probing pulses.Delays up to approximately 200 ns are measured.This is the first time a group delay is observed with a single atom as the delaying medium.iii
We study the dynamics of a system composed of two coupled cavities, each interacting with a single Rydberg atom. The interplay between Rydberg-Rydberg interaction and photon hopping enables the transition of the atoms from the collective ground state to the double Rydberg excitation state by individually interacting with the optical normal modes and suppressing the upconversion process between them. The atomic transition is accompanied by the two-photon absorption and emission of the normal modes. Since the energy level structure of the atom-cavity system is photon number dependent there is only a pair of states being in the two-photon resonance. Therefore, the system can act as a quantum nonlinear absorption filter through the nonclassical quantum process, converting coherent light field into a nonclassical state. Meanwhile, the vacuum field in the cavity inspires the Rydberg atoms to simultaneously emit two photons into the normal mode, resulting in obvious emission enhancement of the mode.
We propose a component-selective scheme for improving two-photon sources in a cavity-coupled two-atom system, where a single cavity mode interacts with two two-level atoms driven by phase-controlled classical fields of the same frequency. By controlling the atomic detunings and driving phase, the system can be tailored toward optimized cavity-field two-photon blockade or strongly correlated fluorescence photon-pair emission. When the two-cavity-photon component is enhanced, the cavity field exhibits optimized two-photon blockade with simultaneous suppression of unwanted one- and three-photon components at a comparable two-photon population. In another parameter regime, strongly correlated fluorescence photon pairs can also be generated from the two atoms by selecting the double-atomic-excitation component in the same two-excitation manifold. This approach provides a route toward high-quality and versatile two-photon sources, with potential applications in few-photon quantum optics and quantum information processing.
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.