Scalable technologies to characterize the performance of quantum devices are crucial to creating large quantum networks and quantum processing units. Chief among the resources of quantum information processing is entanglement. Here we describe the full temporal and spatial characterization of polarization-entangled photons produced by Spontaneous Parametric Down Conversions using an intensified high-speed optical camera, Tpx3Cam. This novel technique allows for precise determination of Bell inequality parameters with minimal technical overhead, as well as novel characterization methods of the spatial distribution of entangled quantum information. This could lead to multiple applications in Quantum Information Science, opening new perspectives for the scalability of quantum experiments. arXiv:1808.06720v2 [quant-ph] 13 Sep 2018 Recent developments have shown that spatial characterization of entangled states with single-photon sensitive cameras provides access to a myriad of new possibilities, such as imaging high-dimensional entanglement [8], generalized Bell inequalities [9] and the study of Einstein-Podolsky-Rosen non-localities [10, 11]. However, these measurements used resource-intensive methods, such as sequential scanning or multiple standalone detectors.Early studies of entanglement with modern imagers used an electron-multiplying CCD (EM-CCD) camera with an effective area of 201 × 201 pixels and frame readout-rate of 5Hz [8].Albeit the EMCCD quantum efficiency was up to 90%, prolonged exposure time of about 1ms, requires this device to operate at very small photon-rates to avoid multiple photons in the same frame. Furthermore, to achieve single-photon level sensitivity the EMCCD camera operated at a low temperature of −85 o C.Further progression on quantum imaging with cameras was achieved using intensified CMOS and CCD cameras [12][13][14][15][16][17]. Flexible readout architectures allow kHz continuous framing rates in CMOS cameras. Additionally, nano-second scale time resolution for single photons can be achieved by gating image intensifiers. For example, an intensified sCMOS camera was used to observe Hong-Ou-Mandel interference [18], where the photons were collected on

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...

Cycling processes are important in many areas of physics ranging from lasers to topological insulators, often offering surprising insights into dynamical and structural aspects of the respective system. Here we report on a quantum-nonlinear wave-mixing experiment where resonant lasers and an optical cavity define a closed cycle between several ground and excited states of a single atom. We show that, for strong atom–cavity coupling and steady-state driving, the entanglement between the atomic states and intracavity photon number suppresses the excited-state population via quantum interference, effectively reducing the cycle to the atomic ground states. The system dynamics then result from transitions within a harmonic ladder of entangled dark states, one for each cavity photon number, and a quantum Zeno blockade that generates antibunching in the photons emitted from the cavity. The reduced cycle suppresses unwanted optical pumping into atomic states outside the cycle, thereby enhancing the number of emitted photons.

According to classical theory, the combined effect of several electromagnetic fields is described under the generic term of interference, where intensity patterns with maxima and minima emerge over space. On the other hand, quantum theory asserts that considering only the expectation value of the total field is insufficient to describe light-matter coupling, and the most widespread explanation highlights the role of quantum fluctuations to obtain correct predictions. We here connect the two worlds by showing that classical interference can be quantum-mechanically interpreted as a bosonic form of super-and subradiance, giving rise to bright and dark states for light modes. We revisit the double-slit experiment and the Mach-Zehnder interferometer, reinterpreting their predictions in terms of collective states of the radiation field. We also demonstrate that quantum fluctuations are not the key ingredient in describing the light-matter quantum dynamics when several vacuum modes are involved. In light of our approach, the unambiguous criterion for the coupling to occur is the presence of nondark states when decomposing the collective state of light. We discuss how the results here discussed could be verified in trapped ion systems or in cross-cavity setups. Finally, we show how the bosonic bright and dark states can be employed to implement quantum gates, which paves the way for the engineering of multimode schemes for universal quantum computing.

We report the implementation of a Duan-Lukin-Cirac-Zoller (DLCZ) protocol heralded single-photon source using an ensemble of cold rubidium simultaneously coupled to two optical cavities, enabling substantial enhancements in photon generation rates.