Peter B R Nisbet-Jones

Frequency ratio of two optical clock transitions in 171Yb+ and constraints on the time variation of fundamental constants.

Singly ionized ytterbium, with ultranarrow optical clock transitions at 467 and 436 nm, is a convenient system for the realization of optical atomic clocks and tests of present-day variation of fundamental constants. We present the first direct measurement of the frequency ratio of these two clock transitions, without reference to a cesium primary standard, and using the same single ion of 171Yb+. The absolute frequencies of both transitions are also presented, each with a relative standard uncertainty of 6×10(-16). Combining our results with those from other experiments, we report a threefold improvement in the constraint on the time variation of the proton-to-electron mass ratio, μ/μ=0.2(1.1)×10(-16)  yr(-1), along with an improved constraint on time variation of the fine structure constant, α/α=-0.7(2.1)×10(-17)  yr(-1).

Highly efficient source for indistinguishable single photons of controlled shape

We demonstrate a straightforward implementation of a push-button like single-photon source, which is based on a strongly coupled atom?cavity system. The device operates intermittently for periods of up to 100??s, with single-photon repetition rates of 1.0?MHz and an efficiency of 60%. Atoms are loaded into the cavity using an atomic fountain, with the upper turning point near the cavitys mode centre. This ensures long interaction times without any disturbances induced by trapping potentials. The latter is the key to reaching deterministic efficiencies as high as obtained in probabilistic photon-heralding schemes. The price to pay is the random loading of atoms into the cavity and the resulting intermittency. However, for all practical purposes, this has a negligible impact as an individual atom may emit up to 100 successive photons.

Single-photon absorption in coupled atom-cavity systems

We show how to capture a single photon of arbitrary temporal shape with one atom coupled to an optical cavity. Our model applies to Raman transitions in three-level atoms with one branch of the transition controlled by a (classical) laser pulse, and the other coupled to the cavity. Photons impinging on the cavity normally exhibit partial reflection, transmission, and/or absorption by the atom. Only a control pulse of suitable temporal shape ensures impedance matching throughout the pulse, which is necessary for complete state mapping from photon to atom. For most possible photon shapes, we derive an unambiguous analytic expression for the shape of this control pulse, and we discuss how this relates to a quantum memory.

Photonic qubits, qutrits and ququads accurately prepared and delivered on demand

Reliable encoding of information in quantum systems is crucial to all approaches to quantum information processing or communication. This applies in particular to photons used in linear optics quantum computing, which is scalable provided a deterministic single-photon emission and preparation is available. Here, we show that narrowband photons deterministically emitted from an atom?cavity system fulfil these requirements. Within their 500?ns coherence time, we demonstrate a subdivision into d time bins of various amplitudes and phases, which we use for encoding arbitrary qu-d-its. The latter is done deterministically with a fidelity >95% for qubits, verified using a newly developed time-resolved quantum-homodyne method.

A Single-Ion Trap with Minimized Ion-Environment Interactions

AbstractWe present a new single-ion endcap trap for high-precision spectroscopy that has been designed to minimize ion–environment interactions. We describe the design in detail and then characterize the working trap using a single trapped

Frequency Comparison of

^{171}{\rm Yb}^{+}

Ion Optical Clocks at PTB and NPL via GPS PPP

171Yb+ ion. Excess micromotion has been eliminated to the resolution of the detection method, and the trap exhibits an anomalous phonon heating rate of