Karim Benmessai

Measurement of the Fundamental Thermal Noise Limit in a Cryogenic Sapphire Frequency Standard Using Bimodal Maser Oscillations

We report observations of the Schawlow-Townes noise limit in a cryogenic sapphire secondary frequency standard. The effect causes a fundamental limit to the frequency stability, and was measured through the novel excitation of a bimodal maser oscillation of a Whispering Gallery doublet at 12.04 GHz. The beat frequency of 10 kHz between the oscillations enabled a sensitive probe for this measurement of fractional frequency instability of 10(-14) tau(-1/2) with only 0.5 pW of output power.

High power solid-state sapphire Whispering Gallery mode maser

We present new results on a cryogenic solid-state maser frequency standard, which relies on the excitation of Whispering Gallery (WG) modes within a doped monocrystalline sapphire resonator (α-Al2O3). Included substitutively within the highest purity HEMEX-grade sapphire crystal lattice are Fe2+ impurities at a concentration of parts per million, an unavoidable result of the manufacturing process. Mass conversion of Fe2+ to Fe3+ ions was achieved by thermally annealing the sapphire in air. Above-threshold maser oscillation was then excited in the resonator at zero applied DC magnetic field by pumping high-Q WG modes coincident in frequency with the Electron Spin Resonance (ESR) energy levels of the Fe3+ spin population. A two stage annealing process was undertaken, resulting in an improvement of six orders of magnitude in output power over the previous best implementation of this scheme, and giving an output seven orders of magnitude more powerful than a typical commercial hydrogen maser. We estimate the limit on the frequency stability due to the Schawlow-Townes fundamental thermal noise limit on the order of 1×10−17/√τ.

Hybrid electron spin resonance and whispering gallery mode resonance spectroscopy of Fe3+ in sapphire

The development of a new era of quantum devices requires an understanding of how paramagnetic dopants or impurity spins behave in crystal hosts. Here, we describe a spectroscopic technique which uses traditional electron spin resonance (ESR) combined with the measurement of a large population of electromagnetic whispering gallery modes. This allows the characterization of the physical parameters of paramagnetic impurity ions in the crystal at low temperatures. We present measurements of two ultrahigh-purity sapphires cooled to 20 mK in temperature, and determine the concentration of Fe3 ions and their frequency sensitivity to a dc magnetic field. Our method is different from ESR in that it is possible to track the resonant frequency of the ion from zero applied magnetic field to any arbitrary value, allowing excellent measurement precision. This high precision reveals anisotropic behavior of the Zeeman splitting. In both crystals, each Zeeman component demonstrates a different g factor.

Four-wave mixing from Fe3 + spins in sapphire

Fe(3+) ions in sapphire exhibit an electron spin resonance which interacts strongly with high-Q whispering gallery modes at microwave frequencies. We report the first observation of a third-order paramagnetic nonlinear susceptibility in such a resonator at cryogenic temperatures and the first demonstration of four-wave mixing using this parametric nonlinearity. This observation of an all-microwave nonlinearity is an enabling step towards a host of quantum measurement and control applications which utilize spins in solids.

Creating traveling waves from standing waves from the gyrotropic paramagnetic properties of Fe3+ ions in a high-Q whispering gallery mode sapphire resonator

We report observations of the gyrotropic change in magnetic susceptibility of the Fe 3+ electron paramagnetic resonance at 12.037GHz (between spin states|1/2 > and |3/2 >) in sapphire with respect to applied magnetic field. Measurements were made by observing the response of the high-Q Whispering Gallery doublet (WGH±17,0,0) in a Hemex sapphire resonator cooled to 5 K. The doublets initially existed as standing waves at zero field and were transformed to traveling waves due to the gyrotropic response.

Investigation of NBTI degradation on power VDMOS transistors under magnetic field

In this paper, we report an experimental evidence of the impact of applied a low magnetic field (B<;100 Gauss) during negative bias temperature instability (NBTI) stress and recovery, on commercial power double diffused MOS transistor (VDMOS). We show that both interface (ΔNit) and oxide trap (ΔNot) induced by NBTI stress decrease by applied magnetic field. This decrease is more pronounced as the magnetic field is high. In addition, the recovery of NBTI induced threshold voltage shift (ΔVth) is relatively important with applied magnetic field.

Frequency Conversion in a High Q-factor Sapphire Whispering Gallery Mode Resonator due to Paramagnetic Nonlinearity

Nonlinear frequency conversion is a well known and widely exploited family of effects in optics, often arising from a Kerr nonlinearity in a crystal medium. Here, we report high stability frequency conversion in the microwave regime due to a χ(3) nonlinearity in sapphire introduced by a dilute concentration of paramagnetic spins. First, we produce a high stability comb from two microwave fields at 12.029 and 12.037 GHz corresponding to two high Q-factor whispering gallery (WG) modes within the electron spin resonance bandwidth of the Fe3+ ion. The resulting comb is generated by a cascaded four-wave mixing effect with a 7.7 MHz repetition rate. Then, by suppressing four-wave mixing by increasing the threshold power, third harmonic generation is achieved in a variety of WG modes coupled to various species of paramagnetic ion within the sapphire.

Controlling the frequency-temperature sensitivity of a cryogenic sapphire maser frequency standard by manipulating Fe3 + spins in the sapphire lattice

To create a stable signal from a cryogenic sapphire maser frequency standard, the frequency-temperature dependence of the supporting whispering gallery mode must be annulled. We report the ability to control this dependence by manipulating the paramagnetic susceptibility of Fe3+ ions in the sapphire lattice. We show that the maser signal depends on other whispering gallery modes tuned to the pump signal near 31 GHz, and the annulment point can be controlled to exist between 5 and 10 K, depending on the Fe3+ ion concentration and the frequency of the pump. This level of control has not been achieved previously and will allow improvements in the stability of such devices.

Spin bath maser in a cryogenically cooled sapphire whispering gallery mode resonator

We report the observation of a mechanism of maser generation in an ensemble of intercoupled, inhomogeneously broadened two-level systems, enhanced by high quality factor electromagnetic cavity modes. In this form of population inversion, an inseparable quantum system leads to cavity-enhanced stimulated emission arising from interactions within an ensemble of two-level systems, as opposed to a traditional ensemble of noninteracting identical three-level systems. The effect is observed in a cryogenically cooled whispering gallery mode sapphire resonator containing dilute Fe

The Fe3+:Al2O3 Whispering Gallery Mode Maser Oscillator

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