Ein optisches Frequenznormal mit kalten und ultrakalten Atomen

[no abstract

Intensity stabilisation of optical pulse sequences for coherent control of laser-driven qubits

We demonstrate a system for intensity stabilisation of optical pulse sequences used in laser-driven quantum control of trapped ions. Intensity instability is minimised by active stabilisation of the power (over a dynamic range of > 104 ) and position of the focused beam at the ion. The fractional Allan deviations in power were found to be < 2.2 × 10−4 for averaging times from 1 to 16,384 s. Over similar times, the absolute Allan deviation of the beam position is < 0.1 μm for a 45 μm beam diameter. Using these residual power and position instabilities, we estimate the associated contributions to infidelity in example qubit logic gates to be below 10−6 per gate

Radio-frequency microplasmas with energies suited to in situ selective cleaning of surface adsorbates in ion microtraps

We have demonstrated a capacitively-coupled, radio-frequency (RF) microplasma inside the 3D electrode structure of an ion microtrap device. For this work, devices with an inter-electrode distance of 340 μm were used. The microplasmas were operated at Ω RF /2π = 23 MHz, in both He and He:N2 gas mixtures, over a range of RF amplitudes (140–220 V) and pressures (250–910 mbar). Spectroscopic analysis of the He I 667 nm and Hα 656 nm emission lines yielded the gas temperature and electron density, which enabled calculation of the mean ion bombardment energy. For the range of operating parameters studied, we calculated mean He+ energies to be between 0.3 and 4.1 eV. While these energies are less than the threshold for He sputtering of hydrocarbon adsorbates on Au, we calculate that the high energy tail of the distribution should remove adsorbate monolayers in as little as 1 min of processing. We also calculate that the distribution is insufficiently energetic to have any significant effect on the Au electrode surface within that duration. Our results suggest that the microplasma technique is suited to in situ selective removal of surface adsorbates from ion microtrap electrodes

Photoassociation spectroscopy of cold calcium atoms

Photoassociation spectroscopy experiments on 40Ca atoms close to the dissociation limit 4s4s 1S0 - 4s4p 1P1 are presented. The vibronic spectrum was measured for detunings of the photoassociation laser ranging from 0.6 GHz to 68 GHz with respect to the atomic resonance. In contrast to previous measurements the rotational splitting of the vibrational lines was fully resolved. Full quantum mechanical numerical simulations of the photoassociation spectrum were performed which allowed us to put constraints on the possible range of the calcium scattering length to between 50 a_0 and 300 a_0

Accurate and agile digital control of optical phase, amplitude and frequency for coherent atomic manipulation of atomic systems

We demonstrate a system for fast and agile digital control oflaser phase, amplitude and frequency for applications in coherent atomicsystems. The full versatility of a direct digital synthesis radiofrequencysource is faithfully transferred to laser radiation via acousto-opticmodulation. Optical beatnotes are used to measure phase steps up to 2π,which are accurately implemented with a resolution of ≤ 10 mrad. By linearizing the optical modulation process, amplitude-shaped pulses of durations ranging from 500 ns to 500 ms, in excellent agreement with the programmed functional form, are demonstrated. Pulse durations are limited only by the 30 ns rise time of the modulation process, and a measured extinction ratio of > 5 × 1011 is achieved. The system presented here was developed specifically for controlling the quantum state of trapped ions with sequences of multiple laser pulses, including composite and bichromatic pulses. The demonstrated techniques are widely applicable to other atomic systems ranging across quantum information processing,frequency metrology, atom interferometry, and single-photon generation

Low-noise synthesis of microwave signals from an optical source

The low-noise synthesis of a harmonic comb of microwave frequencies using a 1 GHz femtosecond-laser-based synthesiser that is referenced to a cavity-stab ilised laser is demonstrated. The residual phase noise is ~ 110 dBcjHz at 1 Hz offset from the 10 GHz harmonic. Phase noise is measured with an interferometric measurement system having low sensitivity to AM

Femtosecond-Iaser-based synthesis of ultrastable microwave signals from optical frequency references

We use femtosecond laser frequency combs to convert optical frequency references to the microwave domain, where we demonstrate the synthesis of lO-GHz signals having a fractional frequency instability of ~ 3 . 5 X 10-15 at a 1-s averaging time, limited by the optical reference. The residual instability and phase noise of the femtosecond-laser-based frequency synthesizers are 6.5X 10-16 at 1 sand - 98 dBc/Hz at a I-Hz offset from the lO-GHz carrier, respectively. The timing jitter of the microwave signals is 3.3 fs

Optical Frequency Synthesis and Comparison with Uncertainty at the 10 -19 Level

A femtosecond Laser-based opticaL frequency synthesizer is referenced to an optical standard, and we use it to demonstrate the generation and controL of the frequency of eLectromagnetic fieLds over 100 terahertz of bandwidth with fractionaL uncertainties approaching 1 part in 10 19. The reproducibility of this performance is verified by comparison of different types of femtosecond Laserbased frequency synthesizers from three Laboratories

Frequency Uncertainty for Optically Referenced Femtosecond Laser Frequency Combs

We present measurements and analysis of the currently known relative frequency uncertainty of femtosecond laser frequency combs (FLFCs) based onKerr-lens mode-locked Ti:sapphire lasers. Broadband frequency combs generated directly from the laser oscillator, as well as octave-spanning combs generated with nonlinear optical fiber are compared. The relative frequency uncertainty introduced by an optically referenced FLFC is measured for both its optical and microwave outputs. We find that the relative frequency uncertainty of the optical and microwave outputs of the FLFC can be as low as 8 x 10 -20 and 1.7 x 10 -18, with a confidence level of 95%, respectively. Photo-detection of the optical pulse train introduces a small amount of excess noise, which degrades the stability and subsequent relative frequency uncertainty limit of the microwave output to 2.6 x 10 -17

Absolute frequency measurement of the neutral 40Ca optical frequency standard at 657 nm based on microkelvin atoms

We report an absolute frequency measurement of the optical clock transition at 657 nm in 40Ca with a relative uncertainty of 7.5 x 10-15 , one of the most accurate frequency measurements of a neutral atom optical transition to date. The frequency (455986240494135.8 ± 3.4) Hz was measured by stabilizing a diode laser system to a spectroscopic signal derived from an ensemble of 106 atoms cooled in two stages to a temperature of 10 flK. The measurement used a femtosecond-laser-based frequency comb to compare the Ca transition frequency with that of the single-ion 199Hg+ optical frequency standard at NIST. The Hg+ frequency was simultaneously calibrated relative to the NIST Cs fountain via the NIST time scale to yield an absolute value for the Ca transition frequency. The relative fractional instability between the two o~tical standards was 2 x 10-15 for 10 s of averagmg tIme and 2 x 10-1 for 2000 s