Continuous Generation of Quantum Light from a Single Ground-State Atom in an Optical Cavity

Abstract

We show an optical wave-mixing scheme that generates quantum light by means of a single three-level atom. The atom couples to an optical cavity and two laser fields that together drive a cycling current within the atom. Weak driving in combination with strong atom-cavity coupling induces transitions between the dark states of the system, accompanied by single-photon emission and suppression of atomic excitation by quantum interference. For strong driving, the system can generate coherent or Schrödinger cat-like fields with frequencies distinct from those of the applied lasers.Many scientific and technological advances during the last decades, across diverse areas of human knowledge, can be associated to the manipulation of light-matter interaction and the generation of light fields in particular. One such achievement is the laser [1]. Here a photon stimulates an atom to decay into the ground state at the expense of the emission of another photon. To amplify this process, the emitting medium (atoms) is placed inside an optical resonator where the repeated reflection of the light allows for a sufficiently strong coupling between the atoms and the field [2]. By decreasing the volume of the optical resonator it is possible to reach a regime where a single atom and a single photon interact strongly, forming an atom-photon molecule. This establishes the research field known as cavity quantum electrodynamics (cavity QED) [3][4][5][6][7][8][9] where the atom-light interaction is controlled at its most fundamental level. Integrating the phenomenon of electromagnetically induced transparency (EIT) [10-12] adds additional capabilities such as allowing an opaque cavity QED system to become transparent [13][14][15][16]. The origin of this effect lies in the destructive interference of different absorption paths, preventing light from being absorbed by the system. We exploit this situation with a three-level atom in a Λ-type level configuration (one excited and two ground states) where one branch is strongly coupled to a mode of an optical resonator and the other to an external laser. In the EIT regime, the system remains in a state known as a dark state, since the atom does not absorb light from the fields.Here we show that this scheme can be used to continuously generate light that is genuinely quantum in nature. To this end, we introduce a second laser field which couples the two ground states. As expected for several waves interacting with a nonlinear medium, this gives rise to a new radiation field via an optical wave mixing process [17][18][19][20][21]. Not expected, however, is that if the laser field coupling the atomic ground states is weak enough, the fragile dark states of the cavity EIT system are not destroyed, even when all fields are on resonance with the respective atomic transitions. We then find that the two lasers in combination with the cavity drive transitions between dark states that differ by one photon in the cavity. Thus, the atomic excitation is suppressed due to the destructive interference of the EI...

Time-ordering effects in a one-atom laser based on electromagnetically-induced transparency

“…One of the main limiting factors for producing highly nonclassical optical states in OAL is spontaneous decay from the excited atomic level. Recently, it was suggested [13] to use the technique of electromagnetically-induced transparency (EIT) [14][15][16][17][18][19][20] in OAL, employing an atom in Λ-configuration with two ground and one excited state. In this configuration, under conditions of EIT, the population of the excited state of the atom is very low, which dramatically decreases the influence of its spontaneous decay on the operation of the laser.…”

“…We note that the model of Ref. [13] disregards the time ordering in the evolution operator, which is a good approximation for a small number of photons in the cavity only. Generation of superpositions of two macroscopically (or at least mesoscopically) distinguishable states, known as optical analogs of the Schrödinger cat state, may thus require considering the time-ordering effects in the evolution of a quantum system with a time-dependent Hamiltonian [22,23].…”

“…II we give a general description of the considered system and deduce the effective Hamiltonian and the atom-field state without time-ordering, mainly following Ref. [13].…”

Continuous quantum light from a dark atom

“…In this case the entanglement of the atomic ground states with the photon number in the cavity effectively preserves the destructive interference of atomic excitation amplitudes, and thus, the dark states. The possibility to have any number of photons in the cavity furthermore produces an infinite harmonic ladder of dark states that can be used to produce either quantum or coherent light [11]. Replacing a laser with a cavity has the further advantage that it introduces in the otherwise decoherence-free subspace in which the system operates, a well-defined dissipation channel through which the system dynamics can be observed in real time.…”

Emergence of Non-Gaussian Coherent States Through Nonlinear Interactions

“…Non-classical states of light can be harvested for a range of uses, from increasing the precision of a measurement to processing information beyond what is possible with classical resources [5][6][7][8][9]. However, such quantum states are naturally uncommon, and generating them requires a variety of specialized experimental settings that rely on nonlinear interactions between the EM field and matter [10][11][12][13]. Considering the applications and demand for intense, macroscopic, non-classical light across different platforms, it becomes relevant to understand the minimal conditions to extract useful quantum properties from the more common, yet still quantum, coherent states of light.…”