2,346 research outputs found
Comment on "Test of constancy of speed of light with rotating cryogenic optical resonators"
A recent experiment by Antonini et. al. [Phys. Rev. A {\bf 71}, 050101R
2005], set new limits on Lorentz violating parameters in the frame-work of the
photon sector of the Standard Model Extension (SME),
, and the Robertson-Mansouri-Sexl (RMS) framework,
. The experiment had significant systematic effects caused by
the rotation of the apparatus which were only partly analysed and taken into
account. We show that this is insufficient to put a bound on
and the bound on represents a
five-fold improvement not a ten-fold improvement as claimed.
(For reply see Phys. Rev. A 72, 066102 (2005) DOI:
10.1103/PhysRevA.72.066102)Comment: 2 page
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 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 -factor
Whispering Gallery (WG) modes within the Electron Spin Resonance (ESR)
bandwidth of the Fe 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
High Resolution Flicker-Noise-Free Frequency Measurements of Weak Microwave Signals
Amplification is usually necessary when measuring the frequency instability
of microwave signals. In this work, we develop a flicker noise free frequency
measurement system based on a common or shared amplifier. First, we show that
correlated flicker phase noise can be cancelled in such a system. Then we
compare the new system with the conventional by simultaneously measuring the
beat frequency from two cryogenic sapphire oscillators with parts in 10^15
fractional frequency instability. We determine for low power, below -80 dBm,
the measurements were not limited by correlated noise processes but by thermal
noise of the readout amplifier. In this regime, we show that the new readout
system performs as expected and at the same level as the standard system but
with only half the number of amplifiers. We also show that, using a standard
readout system, the next generation of cryogenic sapphire oscillators could be
flicker phase noise limited when instability reaches parts in 10^16 or betterComment: Accepted for publication in IEEE Transactions on Microwave Theory &
Technique
High Q-factor Sapphire Whispering Gallery Mode Microwave Resonator at Single Photon Energies and milli-Kelvin Temperatures
The microwave properties of a crystalline sapphire dielectric whispering
gallery mode resonator have been measured at very low excitation strength
(E/hf=1) and low temperatures (T = 30 mK). The measurements were sensitive
enough to observe saturation due to a highly detuned electron spin resonance,
which limited the loss tangent of the material to about 2e-8 measured at 13.868
and 13.259 GHz. Small power dependent frequency shifts were also measured which
correspond to an added magnetic susceptibility of order 1e-9. This work shows
that quantum limited microwave resonators with Q-factors > 1e8 are possible
with the implementation of a sapphire whispering gallery mode system
- âŠ