We have measured the current-phase relationship I(ϕ) of symmetric 45 • YBa2Cu3O7−x grain boundary Josephson junctions. Substantial deviations of the Josephson current from conventional tunnel-junction behavior have been observed: (i) The critical current exhibits, as a function of temperature T , a local minimum at a temperature T * . (ii) At T ≈ T * , the first harmonic of I(ϕ) changes sign. (iii) For T < T * , the second harmonic of I(ϕ) is comparable to the first harmonic, and (iv) the ground state of the junction becomes degenerate. The results are in good agreement with a microscopic model of Josephson junctions between d-wave superconductors.The most important phenomenological difference between the high-T c cuprates and conventional superconductors regards the orbital symmetry of the superconducting order parameter. In the cuprates the pair potential changes sign depending on the direction in momentum space according to 1,2 ∆(ϑ) = ∆ 0 cos 2(ϑ − θ), where ϑ is the angle between the wave vector and the (laboratory) x-axis, while θ is the angle between the Cu-Cu bond direction of the superconductor and the x-axis. This unconventional d-wave symmetry was predicted 3 and experimentally confirmed 1,2 to be directly measurable in the Josephson effect between a high-T c and a conventional superconductor. Another consequence of the dwave symmetry is that mid-gap states (MGS) with energy ε = 0 should form on the free surface of a d-wave superconductor if ∆(ϑ) has opposite signs on incident and reflected electronic trajectories. 4 The MGS density must be maximal for (110)-like surfaces and this prediction has in fact been confirmed by STM microscopy on YBCO single crystals 5 which revealed the MGS contribution to the YBCO tunneling density of states. The presence of the MGS is expected to influence in a spectacular way also the Josephson effect in junctions between d-wave superconductors with different crystallographic orientations. Yet no clear manifestation of the MGS in the Josephson effect in such junctions has been observed so far, which is a challenge for the concept of d-wave superconductivity in the cuprates.Moreover, due to possible applications in quantum computing, 6,7 there is substantial interest in Josephson junctions and circuits with a doubly degenerate ground state. Such a state was predicted in an asymmetric 45 • junction (θ 1 = 0 • and θ 2 = 45 • , the angles θ 1,2 are defined in Fig. 1), since odd harmonics of the Josephson current I(ϕ) = n I n sin nϕ are suppressed by symmetry. 8,9The current-phase relation observed in Ref. 10 indeed showed a substantial contribution of the second harmonic I 2 . However, there is a finite supercurrent flowing along the interface in the ground state of asymmetric 45 • junctions. 9 Therefore they do not lead to completely quiet qubits in the sense of Ref. 6. Motivated by the search for both, the MGS in high-T c Josephson junctions and a quiet qubit, we have studied symmetric 45 • junctions (i.e. junctions with θ 1 = −θ 2 = 22.5 • ). In this paper we report the fir...

We present an optically pumped magnetometer working in a new operational mode—the light-shift dispersed Mz (LSD-Mz) mode. It is realized combining various features; (1) high power off-resonant optical pumping; (2) Mz configuration, where pumping light and magnetic field of interest are oriented parallel to each other; (3) use of small alkali metal vapor cells of identical properties in integrated array structures, where two such cells are pumped by circularly polarized light of opposite helicity; and (4) subtraction of the Mz signals of these two cells. The LSD-Mz magnetometer’s performance depends on the inherent and very complex interplay of input parameters. In order to find the configuration of optimal magnetometer resolution, a sensitivity analysis of the input parameters by means of Latin Hypercube Sampling was carried out. The resulting datasets of the multi-dimensional parameter space exploration were assessed by a subsequent physically reasonable interpretation. Finally, the best shot-noise limited magnetic field resolution was determined within that parameter space. As the result, using two 50 mm3 integrated vapor cells a magnetic field resolution below 10 fT/√Hz at Earth’s magnetic field strength is possible.

The current-phase relation (CPR) for asymmetric 45 • Josephson junctions between two d-wave superconductors has been predicted to exhibit an anomalous periodicity. We have used the singlejunction interferometer to investigate the CPR for this kind of junctions in YBa2Cu3O7−x thin films. Half-fluxon periodicity has been experimentally found, providing a novel source of evidence for the d-wave symmetry of the pairing state of the cuprates.

We demonstrate a way of operating an optically pumped magnetometer with miniaturized cesium cell using the light-narrowing effect. The magnetometer setup shows improvement of shot-noise-limited sensitivity (42 fT/ √ Hz in a cell of only 9.3 mm 3 volume) due to the suppression of spin-exchange relaxation to a large extent and the use of a strikingly increased fraction of alkali-metal atoms for signal generation, working even in μT magnetic fields, by using only a single high-intensity laser beam both for pumping and probing of atomic spins.

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We compare the performance of two methods for the synchronization of the atomic spins in optically pumped magnetometers: intensity modulation of the pump light and the classical M(x) method using B(1) field modulation. Both techniques use the same set-up and measure the resulting features of the light after passing a micro-fabricated Cs cell. The intensity-modulated pumping shows several advantages: better noise-limited magnetic field sensitivity, misalignment between pumping and spin synchronization is excluded, and magnetometer arrays without any cross-talk can be easily set up.

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When optically pumped magnetometers are aimed for the use in Earth's magnetic field, the orientation of the sensor to the field direction is of special importance to achieve accurate measurement result. Measurement errors and inaccuracies related to the heading of the sensor can be an even more severe problem in the case of special operational configurations, such as for example the use of strong off-resonant pumping. We systematically study the main contributions to the heading error in systems that promise high magnetic field resolutions at Earth's magnetic field strengths, namely the non-linear Zeeman splitting and the orientation dependent light shift. The good correspondence of our theoretical analysis to experimental data demonstrates that both of these effects are related to a heading dependent modification of the interaction between the laser light and the dipole moment of the atoms. Also, our results promise a compensation of both effects using a combination of clockwise and counter clockwise circular polarization.