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Experimental demonstration of enhanced-sensitivity Grover-Michelson interferometer for quantum sensing

Christopher R. Schwarze, David S. Simon, Anthony D. Manni, Abdoulaye Ndao, Alexander V. Sergienko

Published Jan 1, 2025• 0 citations
Publisher

Abstract

We construct and characterize a Grover coin with tabletop optics. This directionally unbiased higher-dimensional four-port scatterer replaces a standard beam-splitter in the Michelson interferometer, resulting in a sharper phase response without reducing visibility.
DOI
10.1364/cleo_fs.2025.ff120_3

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•Jan 1, 2023•0 citations
We present a low-resource and robust optical implementation of the four-dimensional Grover coin, a four-port linear-optical scatterer that augments the low dimensionality of a regular beam-splitter. While prior realizations of the Grover coin required a potentially unstable ring cavity to be formed, this version of the scatterer does not exhibit any internal interference. When this Grover coin is placed in another system, it can be used for interferometry with a higher-dimensional set of optical field modes. In this case, we formed a Grover-Michelson interferometer, which results when the traditional beam-splitter of a Michelson interferometer is replaced with a four-port Grover coin. This replacement has been shown to remove a phase parameter redundancy in the original Michelson system, now allowing continuous tuning of the shape and slope of the interference pattern. We observed an intensity interferogram with 97% visibility and a phase sensitivity more than an order of magnitude larger than a regular Michelson interferometer. Because this device is readily formed with nearly the same number of optomechanical resources as a Michelson interferometer but can outperform it drastically in phase delay evaluation, it has a great potential to improve many interferometric sensing and control systems.
The Michelson interferometric phase detection resolution can be enhanced by replacing conventional beam splitters with novel directionally unbiased four-port scatterers, such as Grover coins. We present a quantitative analysis of the noise-to-signal ratio of sideband frequencies generated by gravitational wave-induced phase perturbations in a Grover-Michelson interferometer (GMI). We discuss the principles of GMI signal enhancement and demonstrate how combining this configuration with additional light-recycling arrangements further enhances the performance.
Here we introduce interferometric devices by combining optical feedback (cavities) with unbiased multiports, which, unlike traditional beam dividers, allow light to reflect back out of the port from which it originated. By replacing the traditional, directionally biased beam-splitter in a Michelson interferometer with an unbiased multiport, the functional dependence of the scattering amplitudes changes. As a result, the derivative of transmittance with respect to an external phase perturbation can be made substantially large. This significantly enhances the resolution of phase measurement and allows the phase response curves to be altered in real time by tuning an externally controllable phase shift.
Grover multiports are higher-dimensional generalizations of beam splitters, in which input to any one of the four ports has equal probability of exiting at any of the same four ports, including the input port. In this paper, we demonstrate that interferometers built from such multiports have novel features. For example, when combined with two-photon input and coincidence measurements, it is shown that such interferometers have capabilities beyond those of standard beam-splitter-based interferometers, such as easily controlled interpolation between Hong-Ou-Mandel (HOM) and anti-HOM behavior. Further, it is shown that the Grover-based analog of the Mach-Zehnder interferometer can make three separate phase measurements simultaneously. By arranging the transmission lines between the two multiports to lie in different planes, the same interferometer acts as a higher-dimensional Sagnac interferometer, allowing rotation rates about three different axes to be measured with a single device.
We demonstrate a nontraditional design of the Sagnac interferometer by replacing the commonly used beam splitter with a linear-optical Grover multiport. This substitution creates a pole at the origin of the device parameter space, with an associated resonance in the output intensity. The structure of this resonance is dictated only by the nonreciprocal portion of the phase acquired in the Sagnac loop. This property directly results from adopting the more symmetric and higher-dimensional central scattering coin, and it allows for a different approach to registering and detecting the nonreciprocal Sagnac phase. This parameter may be extracted from the width of a peak or dip in the interferogram, instead of tracing small changes in power as in traditional Sagnac interferometry. We discuss how losses affect the system and potential metrological applications.
Recent advances in linear quantum optics have involved the development of unbiased, multi-port optical elements for use with pairs of identical photons, or biphotons, for the design of novel quantum devices. The unbiased counterpart of a conventional 50:50 beam-splitter is a particularly useful multiport, thanks to its unique algebraic properties when acting on both classical and quantum states of light. Dubbed the “Grover coin” due to its utility in the Grover’s Search quantum algorithm, the unbiased four-port behaves as a conventional beam splitter, but with two additional ports to provide a photon amplitude with four, equally-probable, spatially distinct paths through which it may propagate. While the Grover coin has been realized in the laboratory in the form of bulk optical elements, the formation of a network of Grover coins is impractical due to the meticulous alignment and large number of elements required for a single component. Therefore, the development of a small, chip-integrated embodiment of the unbiased four-port would enable experimentation with novel quantum optics theories, through the interconnection of multiple Grover coins over a small footprint. This thesis details the design and fabrication of photonic waveguide-based integrated circuit elements through numerical simulation, topology optimization and CMOS-compatible manufacturing processes.