The extraordinary concept of weak value amplification and a number of other seemingly
counter-intuitive wave phenomena are manifestations of fine interference effects.
In this report, we show that weak value amplification naturally arises in the cases of
nearly destructive interference between the two orthogonal states of the observable which
mimics the corresponding near destructive interference between the eigenstates of the
measuring observable as a consequence of nearly mutually orthogonal pre and post selections
of the system states. In order to elucidate this, we first experimentally demonstrate
a weak measurement concept that uses near destructive interference of two paths
of an interferometer having slightly rotated linear polarization states of light. By generating
nearly destructive interference between the two paths with small amplitude and
phase offsets of the waves, we observe both real and imaginary (respectively) weak value
amplification of the small polarization rotation leading to large rotation of the polarization
vector orientation and dramatic changes in the circular polarization descriptor
fourth Stokes vector element of light, respectively. We go on to demonstrate that the giant
enhancement of magneto-optical Kerr rotation, by which we can claim that we have
found a non-modulation based and cost-effective magneto-optical Kerr effect (MOKE)
measurement. At the end, we show successful weak value amplification of spin Hall shift
in magneto-optical sample in both longitudinal and polar MOKE. Our ongoing work is
to find out the relation between magneto-optical Kerr rotation and spin Hall shift of light
in magnetic material.
The extraordinary concept of weak value amplification and a number of other seemingly
counter-intuitive wave phenomena are manifestations of fine interference effects.
In this report, we show that weak value amplification naturally arises in the cases of
nearly destructive interference between the two orthogonal states of the observable which
mimics the corresponding near destructive interference between the eigenstates of the
measuring observable as a consequence of nearly mutually orthogonal pre and post selections
of the system states. In order to elucidate this, we first experimentally demonstrate
a weak measurement concept that uses near destructive interference of two paths
of an interferometer having slightly rotated linear polarization states of light. By generating
nearly destructive interference between the two paths with small amplitude and
phase offsets of the waves, we observe both real and imaginary (respectively) weak value
amplification of the small polarization rotation leading to large rotation of the polarization
vector orientation and dramatic changes in the circular polarization descriptor
fourth Stokes vector element of light, respectively. We go on to demonstrate that the giant
enhancement of magneto-optical Kerr rotation, by which we can claim that we have
found a non-modulation based and cost-effective magneto-optical Kerr effect (MOKE)
measurement. At the end, we show successful weak value amplification of spin Hall shift
in magneto-optical sample in both longitudinal and polar MOKE. Our ongoing work is
to find out the relation between magneto-optical Kerr rotation and spin Hall shift of light
in magnetic material.
The extraordinary concept of weak value amplification and a number of other seemingly counter-intuitive wave phenomena are manifestations of fine interference effects. Taking example of one such intriguing wave interference phenomenon, namely, optical Fano resonance, we show that weak value amplification naturally arises in such scenario due to near destructive spectral interference between a continuum mode and a narrow resonance mode which mimics the corresponding near destructive interference between the eigenstates of the measuring observable as a consequence of nearly mutually orthogonal pre and post selections of the system states. In order to elucidate this, we first experimentally demonstrate a weak measurement concept that uses near destructive interference of two paths of an interferometer having slightly rotated linear polarization states of light. By generating nearly destructive interference between the two paths with small amplitude and phase offsets of the waves, we observe both real and imaginary (respectively) weak value amplification of the small polarization rotation leading to large rotation of the polarization vector orientation and dramatic changes in the circular polarization descriptor 4th Stokes vector element of light, respectively. We go on to demonstrate that the giant enhancement of small Faraday rotation in the vicinity of the Fano spectral dip in waveguided magneto-plasmonic crystal is a manifestation of such natural interferometric weak value amplification.
The extraordinary concept of weak value amplification can be formulated within the realm of wave interference as nearly destructive interference between the eigenstates of the measuring observable. Here we report on a phenomenon of interferometric weak value amplification of small polarization rotation in Fano resonance that evolves completely naturally due to near destructive spectral domain interference between a continuum and a narrow resonance mode having slightly different polarization response. In order to elucidate this, we first experimentally demonstrate an interferometric weak value amplification concept by generating nearly destructive interference of two paths of an interferometer having slightly rotated linear polarization states of light. The weak value amplification of polarization rotation effect is manifested as dramatic changes in the polarization state of light, which acts as the pointer. We go on to demonstrate that the manifestation of natural interferometric weak value amplification is an important contributing factor to the observed giant Faraday rotation and ellipticity in waveguided magneto-plasmonic crystals exhibiting prominent Fano resonance. The natural weak value interpretation of the enhanced Faraday rotation in hybrid magneto-plasmonic systems enriches the existing understanding on its origin. This opens up a new paradigm of natural weak measurement for gaining fundamental insights and ensuing practical applications on various weak interaction effects in rich variety of wave phenomena that originate from fine interference effects.
Geometric Spin Hall effect of light (SHEL) has attracted considerable attention because of the universality of this variant of the spin Hall shift and its independence on the light-matter interactions and materials properties. However, the magnitude of geometric SHEL is typically very small, in the sub-wavelength domain, making it difficult for direct experimental observation. Here, we have applied weak measurement schemes to amplify and faithfully observe the geometric SHEL. In our experiment, the input beam is pre-selected in linear polarization basis (p- or slinear polarization) and post selections are done at nearly orthogonal linear polarizations (small angle ϵ away from the exact orthogonal).This results in weak value amplification (~cotϵ) of the resulting shift of the beam centroid. Moreover, this process also leads to selective conversion of spatial to angular nature of geometric SHEL, which along with the weak value amplification leads to manifold amplification of the resulting SHEL, enabling its reliable experimental detection. A key feature of our weak measurement scheme is that both the weak perturbation (tiny geometric SHEL) and the post selection are done simultaneously by a single optical element, namely, a linear polarizer. The dependence of the weak value of the geometric SHEL on the pre and the post selection of polarization states in both linear and elliptical basis were also investigated in details. The specifics of the different weak measurement schemes, various intriguing experimental manifestations of the weak value amplified geometric SHEL, their analysis / interpretation via polarization operator based treatment of weak measurements is presented here.
Background: Weak measurement involves weak coupling between the system and the measuring device (pointer) enables large amplification and high precision measurement of small physical parameters. The outcome of this special measurement procedure involving nearly mutually orthogonal pre- and post-selection of states in such weakly interacting systems leads to weak value that can become exceedingly large and lie outside the eigenvalue spectrum of the measured observable. This unprecedented ability of weak value amplification of small physical parameters has been successfully exploited for various metrological applications in the optical domain and beyond. Even though it is a quantum mechanical concept, it can be understood using the classical electromagnetic theory of light and thus can be realized in classical optics. Objective: Here, we briefly review the basic concepts of weak measurement and weak value amplification, provide illustrative examples of its implementation in various optical domains. The applications involve measuring ultra-sensitive beam deflections, high precision measurements of angular rotation, phase shift, temporal shift, frequency shift and so forth, and expand this extraordinary concept in the domain of nano-optics and plasmonics. Methods: In order to perform weak value amplification, we have used Gaussian beam and spectral response as the pointer subsequently. The polarization state associated with the pointer is used as pre and post-selection device. Results: We reveal the weak value amplification of sub-wavelength optical effects namely the Goos-Hänchen shift and the spin hall shift. Further, we demonstrate weak measurements using spectral line shape of resonance as a natural pointer, enabling weak value amplification beyond the conventional limit, demonstrating natural weak value amplification in plasmonic Fano resonances and so forth. The discussed concepts could have useful implications in various nano-optical systems to amplify tiny signals or effects. Conclusion: The emerging prospects of weak value amplification towards the development of novel optical weak measurement devices for metrological applications are extensively discussed.
Using the profound interferometric philosophy of weak-value amplification, we propose a simple, general, and robust polarization method for the amplification and quantification of small magnitudes of all possible polarization anisotropy effects in a single experimental embodiment. The approach is experimentally realized by introducing a weak coupling between the polarization degree of freedom of light and the path degree of freedom in a Mach-Zehnder interferometer in the presence of a weak anisotropy effect. Real and imaginary weak-value amplifications of different polarization anisotropy effects are manifested as characteristic changes in the relevant Stokes vector elements at the exit port of the interferometer, which follow orthogonal trajectories in the Poincar\'e sphere. The proof-of-concept experiment demonstrates that by using this scheme, one can faithfully extract and quantify an anisotropy parameter that is smaller than the typical sensitivity of measurement of a given Stokes parameter of a traditional polarimeter by a large weak-value amplification factor. This opens up the possibility of a sample measuring weak-value polarimeter for studying the rich variety of fundamental optical effects and for materials characterization and precision metrology.
Magneto-optical (MO) effects, manifested as a complex rotation of light polarization under an external magnetic field, have found renewed and advanced applications in integrated photonics, intelligent sensing, ultrafast magnetic recording, and high-resolution magnetic imaging. Accurate measurement of both the rotation angle (the real part) and the ellipticity (the imaginary part) is essential for fundamental research and device applications. However, existing measurement schemes generally require separate measurements or distinct detection configurations and therefore cannot simultaneously retrieve both quantities in a single measurement. In this work, we propose a scheme based on weak measurement using dual-pointers, enabling the simultaneous measurement of the rotation angle and ellipticity within a single meter state. This method was theoretically and experimentally implemented to measure the magneto-optical Kerr effect (MOKE), the Faraday effect, and the Cotton-Mouton effect, demonstrating its broad applicability. This work contributes a characterization technique for the complex angle of MO effects, supporting potential applications across spintronics, quantum materials, and advanced optical sensing.