Resonant interaction of a single atom with single photons from a down-conversion source

Abstract

We observe the interaction of a single trapped calcium ion with single photons produced by a narrow-band, resonant down-conversion source [A. Haase et al., Opt. Lett. 34, 55 (2009)], employing a quantum jump scheme. Using the temperature dependence of the down-conversion spectrum and the tunability of the narrow source, absorption of the down-conversion photons is quantitatively characterized.PACS numbers: 42.50. Ct, 42.50.Ex, 03.67.Bg At the level of single particles, the quantum nature of light-matter interaction becomes manifest, and the absorption and emission of single photons by single atoms is one of the key physical processes on which quantum optics is built. Seminal examples of phenomena in this respect are photon anti-bunching [1,2], quantum jumps [3,4,5,6], Jaynes-Cummings dynamics [7], and atomphoton entanglement [8,9,10].At the same time, important applications of quantum optics, in particular in quantum optical information technology and in quantum metrology, are based on atom-photon interaction at the single particle level. The most precise clock is realized with a single laser-excited trapped ion [11], and strings of trapped ions have been shown to be promising systems for implementing quantum logical algorithms [12,13,14,15,16] as well as quantum networks [17].A key step in converting quantum optical phenomena into quantum technology tools is the control of the processes at all levels, i.e. of the atomic internal (electronic) and external (motional) state, and of the parameters of the photons, including their spatial and temporal shape, their polarization, and, ideally, their arrival times. Two major strategies may be distinguished how such control is obtained: on the one hand through deterministic operations, whereby typically photons are confined and controlled by high-finesse cavities, on the other hand through probabilistic operations, whereby some experimental signal indicates that the desired interaction process has occurred. Further approaches include collective effects in atomic samples [18,19,20] [33,34], two-and three-ion quantum gates [12,13,35,36], and multi-ion entanglement [14,15]. In terms of control of individual photons, spontaneous parametric down-conversion (SPDC) sources produce entangled photon pairs at high fidelities and rates [37,38], and serve as "heralded" single-photon sources [39].In this context we report the observation of interaction between a single atom and single photons from a spontaneous parametric down-conversion source. The atom in our experiment is a single 40 Ca + ion, trapped in a linear Paul trap and cooled by continuous laser excitation; the photons are produced by a SPDC source, described in more detail in Refs. [40,41], which is tuned to provide entangled photon pairs in the wavelength range of the 4D 3/2 − 4P 3/2 transition in Ca + . In the current experiment we measure the interaction of the single atom with one photon of the entangled pairs by observing quantum jumps, very similar to Dehmelt's proposal for spectroscopy on highly forbidden transi...

Photon entanglement detection by a single atom

“…At the same time, entangled SPDC photon pairs offer robust and simple generation of high-purity entanglement at a large rate and thereby serve as an optimal resource for communication over quantum channels [34][35][36][37]. In our previous work [38,39], we operated for the first time a hybrid quantum system integrating single trapped ions and SPDC photon pairs. We demonstrated absorption of single photons by the ion [38] and showed that the absorption of one photon from a pair can be heralded by the coincident detection of its partner photon [39]; time and frequency correlations of the photon pair are manifested in the heralded absorption process.…”

Heralded mapping of photonic entanglement into single atoms in free space: proposal for a loophole-free Bell test

“…Experimental activities investigating the resonant interaction in free-space of a single atom with single photons produced through the spontaneous parametric down conversion (SPDC) have emerged in parallel [15][16][17]. In [18], the interaction of single heralded SPDC photons with a single atom has been demonstrated and in [19], the possibility of obtaining atom-photon entanglement from the absorption by a single atom of a photon belonging to a polarizationentangled SPDC pair has been shown.…”

“…For concreteness, we consider implementing the scheme using two distant single trapped and laser-cooled 40 Ca + ions. The 40 Ca + ion is the only single atomic system so far which has been coupled to entangled SPDC photons [17][18][19]. A scheme of its relevant atomic levels and transitions is shown in figure 2.…”

“…A scheme of its relevant atomic levels and transitions is shown in figure 2. Based on the experimental work reported in [15][16][17][18][19] we assume that the entangled photons are created at 854 nm, resonant with the transition from the metastable D 5/2 level to P 3/2 . Photon loss in optical fibres at this wavelength is of the order of 1 dB km −1 .…”

Quantum jumps induced by the center-of-mass motion of a trapped atom

“…[11][12][13], and for detecting the quantum state of trapped atoms [13,14]. Most recent experiments used quantum jumps in order to demonstrate single photon absorption by single trapped atoms [15], and analyzed their statistics in order to demonstrate quantum correlations between the absorbed photon and a second, entangled photon revealed at a detector [16]. Further experimental work used quantum jumps in the signal monitoring the number of photons inside a resonator as the basic element for implementing feedback loops, restoring the quantum state of a cavity mode [17].…”