Improving ellipticity detection sensitivity for the Q & A vacuum birefringence experiment (original) (raw)
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Classical and Quantum Gravity, 2004
We have built and tested a 3.5 m high-finesse Fabry-Perot prototype inteferometer with a precision ellipsometer for the QED test and axion search (Q & A) experiment. We use X-pendulum-double-pendulum suspension designs and automatic control schemes developed by the gravitational-wave detection community. Verdet constant and Cotton-Mouton constant of the air are measured as a test. Double modulation with polarization modulation 100 Hz and magneticfield modulation 0.05 Hz gives 10 −7 rad phase noise for a 44-minute integration.
Optical Search for QED vacuum magnetic birefringence, Axions and photon Regeneration
cdsweb.cern.ch
Since its prediction in 1936 by Euler, Heisenberg [3] and Weisskopf [4] in the earlier development of the Quantum Electrodynamic (QED) theory, the Vacuum Magnetic Birefringence (VMB) is still a challenge for optical metrology techniques. According to QED [5], the vacuum behaves as an optically active medium in the presence of an external magnetic field. It can be experimentally probed with a linearly polarized laser beam [6]. After propagating through the vacuum submitted to a transverse magnetic field, the polarization of the laser beam will change to elliptical and the parameters of the polarization are directly related to fundamental constants such as the fine structure constant and the electron Compton wavelength. Contributions to the VMB could also arise from the existence of light scalar or pseudoscalar particles like axions that couple to two photons and this would manifest itself as a sizeable deviation from the initial QED prediction [7]. On one side, the interest in axion search, providing an answer to the strong-CP problem lies beyond particle physics since such hypothetical neutral light spinzero particle is considered as one of the good dark matter candidates, and the only non-supersymmetric one. The cosmological problems concerning dark matter and dark energy could then profit from results obtained from the purely laboratory experiment proposed in this document. On the other side, the domain of physics that will be investigated with this project is guaranteed by the QED vacuum polarization. The test of QED by measuring a predicted ellipticity of the order of 2x10-11 rad for a light beam propagating over ~ 25 km in a 9.5 T field constitutes the best test of a theory never achieved so far i.e. at the level of ∼10-22 that corresponds to the absolute relative change of the vacuum refractive index.
Letter of Intent QED Test and Axion Search by means of Optical Techniques To the CERN SPSC
2006
The re-use of recently decommissioned 15-meter long twin aperture LHC superconducting magnet prototypes, providing a transverse magnetic field B ≈ 9.5 T offers a unique opportunity for the construction of a new powerful two-in-one experiment to investigate the properties of the vacuum by means of optical techniques. Linearly polarised laser light beams will be used as probes inside vacuum chambers housed inside superconducting magnet apertures. One of the apertures will be dedicated to the measurements of the Vacuum Magnetic Birefringence (VMB) and optical absorption anisotropy whereas the other one will be used to detect the photon regeneration from axions or axion-like particles using “a shining light through the wall”. The VMB predicted by the QED theory is expected to be measured for the first time and the CPT symmetry precisely tested. The values or the limiting values of mass and coupling constant to two photons of weakly interacting scalar or pseudo-scalar particles like axio...
Measurements of vacuum magnetic birefringence using permanent dipole magnets: the PVLAS experiment
New Journal of Physics, 2013
The PVLAS collaboration is presently assembling a new apparatus (at the INFN section of Ferrara, Italy) to detect vacuum magnetic birefringence (VMB). VMB is related to the structure of the quantum electrodynamics (QED) vacuum and is predicted by the Euler-Heisenberg-Weisskopf effective Lagrangian. It can be detected by measuring the ellipticity acquired by a linearly polarized light beam propagating through a strong magnetic field. Using the very same optical technique it is also possible to search for hypothetical low-mass particles interacting with two photons, such as axion-like (ALP) or millicharged particles. Here we report the results of a scaled-down test setup and describe the new PVLAS apparatus. This latter is in construction and is based on a highsensitivity ellipsometer with a high-finesse Fabry-Perot cavity (> 4 × 10 5) and two 0.8 m long 2.5 T rotating permanent dipole magnets. Measurements with the test setup have improved, by a factor 2, the previous upper bound on the parameter A e , which determines the strength of the nonlinear terms in the QED 4 Author to whom any correspondence should be addressed. Content from this work may be used under the terms of the Creative Commons Attribution 3.0 licence. Any further distribution of this work must maintain attribution to the author(s) and the title of the work, journal citation and DOI.
Towards a direct measurement of vacuum magnetic birefringence: PVLAS achievements
Optics Communications, 2010
Nonlinear effects in vacuum have been predicted but never observed yet directly. The PVLAS collaboration has long been working on an apparatus aimed at detecting such effects by measuring vacuum magnetic birefringence. Unfortunately the sensitivity has been affected by unaccounted noise and systematics since the beginning. A new small prototype ellipsometer has been designed and characterized at the Department of Physics of the University of Ferrara, Italy entirely mounted on a single seismically isolated optical bench. With a finesse F = 414000 and a cavity length L = 0.5 m we have reached the predicted sensitivity of ψ = 2•10-8 1/√Hz given the laser power at the output of the ellipsomenter of P = 24 mW. This record result demonstrates the feasibility of reaching such sensitivities and opens the way to designing a dedicated apparatus for a first detection of vacuum magnetic birefringence.
Measuring the magnetic birefringence of vacuum: the PVLAS experiment, these proceedings
2016
We describe the principle and the status of the PVLAS experiment which is presently running at the INFN section of Ferrara, Italy, to detect the magnetic birefringence of vacuum. This is related to the QED vacuum structure and can be detected by measuring the ellipticity acquired by a linearly polarized light beam propagating through a strong magnetic field. Such an effect is predicted by the Euler-Heisenberg Lagrangian. The method is also sensitive to other hypothetical physical effects such as axion-like particles and in general to any fermion/boson millicharged particle. Here we report on the construction of our apparatus based on a high finesse (> 2 • 10 5) Fabry-Perot cavity and two 0.9 m long 2.5 T permanent dipole rotating magnets, and on the measurements performed on a scaled down test setup. With the test setup we have improved by about a factor 2 the limit on the parameter Ae describing non linear electrodynamic effects in vacuum: Ae < 2.9 • 10 −21 T −2 @ 95% c.l.
Measuring the Magnetic Birefringence of Vacuum: The Pvlas Experiment
International Journal of Modern Physics A, 2012
We describe the principle and the status of the PVLAS experiment which is presently running at the INFN section of Ferrara, Italy, to detect the magnetic birefringence of vacuum. This is related to the QED vacuum structure and can be detected by measuring the ellipticity acquired by a linearly polarized light beam propagating through a strong magnetic field. Such an effect is predicted by the Euler–Heisenberg Lagrangian. The method is also sensitive to other hypothetical physical effects such as axion-like particles and in general to any fermion/boson millicharged particle. Here we report on the construction of our apparatus based on a high finesse (> 2·105) Fabry–Perot cavity and two 0.9 m long 2.5 T permanent dipole rotating magnets, and on the measurements performed on a scaled down test setup. With the test setup we have improved by about a factor 2 the limit on the parameter Ae describing nonlinear electrodynamic effects in vacuum: Ae < 2.9 · 10-21 T-2 @ 95% C.L.
Modern Physics Letters A, 2007
A number of experiments are underway to detect vacuum birefringence and dichroism — PVLAS, Q & A, and BMV. Recently, PVLAS experiment has observed optical rotation in vacuum by a magnetic field (vacuum dichroism). Theoretical interpretations of this result include a possible pseudoscalar–photon interaction and the existence of millicharged fermions. Here, we report the progress and first results of Q & A (QED [quantum electrodynamics] and Axion) experiment proposed and started in 1994. We use a 3.5-m high-finesse (around 30,000) Fabry–Perot prototype detector extendable to 7-m with the cavity mirrors suspended using X-pendulum-double pendulums. To polarize the vacuum, we use a 2.3-T dipole permanent magnet rotated at 5–10 rev/s, with 27-mm-diameter clear borehole and 0.6-m field length. Our ellipsometer/polarization-rotation-detection-system is formed by a pair of Glan–Taylor type polarizing prisms with extinction ratio lower than 10-8 together with a polarization modulating Faraday...