[en] Rydberg states are used in our one atom Maser experiment because they offer a large dipole moment and couple strongly to low numbers of microwave photons in a high-Q cavity. Here, we report the absolute frequencies of the P_3/2 states for principal quantum numbers n = 36-63. These measurements were made with a three step laser excitation scheme. A wavemeter was calibrated against a frequency comb to provide accurate absolute frequency measurements over the entire range, reducing the measurement uncertainty to 1 MHz. We compare the spectroscopic results with known frequency measurements as a test of measurement accuracy.

[en] High-efficiency single photon detection is an interesting problem for many areas of physics, including low temperature measurement, quantum information science and particle physics. For optical photons, there are many examples of devices capable of detecting single photons with high efficiency. However reliable single photon detection of microwaves is very difficult, principally due to their low energy. In this paper, we present the theory of a cascade amplifier operating in the microwave regime that has an optimal quantum efficiency of 93%. The device uses a microwave photon to trigger the stimulated emission of a sequence of atoms where the energy transition is readily detectable. A detailed description of the detector's operation and some discussion of the potential limitations of the detector are presented.

[en] A new heuristic model of interaction of an atomic system with a gravitational wave (GW) is proposed. In it, the GW alters the local electromagnetic field of the atomic nucleus, as perceived by the electron, changing the state of the system. The spectral decomposition of the wave function is calculated, from which the energy is obtained. The results suggest a shift in the difference of the atomic energy levels, which will induce a small detuning to a resonant transition. The detuning increases with the quantum numbers of the levels, making the effect more prominent for Rydberg states. We performed calculations on the Rabi oscillations of atomic transitions, estimating how they would vary as a result of the proposed effect. (paper)

[en] The Mermin inequality provides a criterion for experimentally ruling out local-realistic descriptions of multiparticle systems. A violation of this inequality means that the particles must be entangled, but does not, in general, indicate whether N-partite entanglement is present. For this, a stricter bound is required. Here we discuss this bound and use it to propose two different schemes for demonstrating N-partite entanglement with atoms. The first scheme involves Bose-Einstein condensates trapped in an optical lattice and the second uses Rydberg atoms in microwave cavities.

[en] A three-step laser excitation scheme is used to make absolute frequency measurements of highly excited nF_7/2 Rydberg states in ⁸⁵Rb for principal quantum numbers n=33-100. This work demonstrates the first absolute frequency measurements of rubidium Rydberg levels using a purely optical detection scheme. The Rydberg states are excited in a heated Rb vapour cell and Doppler-free signals are detected via purely optical means. All of the frequency measurements are made using a wavemeter that is calibrated against a Global Positioning System (GPS)-disciplined self-referenced optical frequency comb. We find that the measured levels have a very high frequency stability, and are especially robust against electric fields. The apparatus has allowed measurements of the states to an accuracy of 8.0 MHz. The new measurements are analysed by extracting the modified Rydberg-Ritz series parameters.