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Metasurfaces have recently opened up applications in the quantum regime, including quantum tomography and the generation of quantum entangled states. With their capability to store a vast amount of information by utilizing the various geometric degrees of freedom of nanostructures, metasurfaces are expected to be useful for processing quantum information. Here, we propose and experimentally demonstrate a programmable metasurface capable of performing quantum algorithms using both classical and quantum light with single photons. Our approach encodes multiple programmable quantum algorithms and operations, such as Grover's search algorithm and the quantum Fourier transform, onto the same metalens array on a metasurface. A spatial light modulator selectively excites different sets of metalenses to carry out the quantum algorithms, while the interference patterns captured by a single-photon camera are used to extract information about the output state at the selected output directions. Our programmable quantum metasurface approach holds promising potential as a cost-effective means of miniaturizing components for quantum computing and information processing.

We develop an approach to map the quantum optical scattering of linear dissipative metasurfaces to Liouvillian dynamics, based on the effective Hamiltonian of the metasurfaces in a fictitious time. Our approach enables us to specify the generalized eigenspace of the Liouvillian superoperator, allowing us to analytically obtain the input-output relationship of the density matrix and the photon transition probabilities. This work facilitates the straightforward modeling of non-Hermitian metasurfaces in the quantum regime, directly from the specification of classical scattering matrix. © 2023, META Conference. All rights reserved.

We propose and experimentally demonstrate a programmable matrix computation in the optical domain using a spatial light modulator (SLM) and a metalens array. Our scheme encodes the programmable matrix to the metalens array by superimposing multiple phase gradients. Meanwhile, the SLM produces a phase-controlled spatial illuminated light which acts as our phase-controlled spatial illuminated light which acts as our input vector. Then, the result can be extracted from the far-field interference pattern constructed by different metalenses using a pattern recognition method. © 2023, META Conference. All rights reserved.

Two-photon interference is an important effect that is tightly related to the quantum nature of light. Recently, it has been shown that the photon bunching from the Hong-Ou-Mandel (HOM) effect can be used for quantum imaging in which sample properties (reflection/transmission amplitude, phase delay, or polarization) can be characterized at the pixel-by-pixel level. In this work, we perform Jones matrix imaging for an unknown object based on two-photon interference. By using a reference metasurface with panels of known polarization responses in pairwise coincidence measurements, the object's polarization responses at each pixel can be retrieved from the dependence of the coincidence visibility as a function of the reference polarization. The post-selection of coincidence images with specific reference polarization in our approach eliminates the need in switching the incident polarization and thus parallelized optical measurements for Jones matrix characterization. The parallelization in preparing input states, prevalent in any quantum algorithms, is an advantage of adopting two-photon interference in Jones matrix imaging. We believe our work points to the usage of metasurfaces in biological and medical imaging in the quantum optical regime.

Metasurfaces provide a promising route for structuring light and generating holograms with designed amplitude, phase, and polarization profiles, leading to a versatile platform for integrating and constructing optical components beyond the conventional ones. At the same time, incorporating coincidence in imaging allows a high signal-to-noise ratio for imaging in very low light levels. As beneficial from the recent development in both metasurfaces and single-photon avalanche diode (SPAD) cameras, we combine the polarization-sensitive capability of metasurfaces with Hong-Ou-Mandel (HOM)-type interference in generating images with tailor-made two-photon interference and polarization coincidence signatures. By using orthogonal linear-polarized photons as incidence, correlated, anticorrelated, and uncorrelated polarization coincidence features can be observed within the same image from the pairwise second-order coherence statistics across different pixels of the image. Our work adds polarization to the demonstrated amplitude and phase sensitivity in the domain of “HOM microscopy” and can be useful for biological and security applications.

Metasurfaces with ultrathin artificial structures have attracted much attention because of their unprecedented capability in light manipulations. The recent development of metasurfaces with controllable responses opens up new opportunities in various applications. Moreover, metasurfaces composed of twisted chiral structures can generate asymmetric responses for opposite incidence, leading to more degrees of freedom in wave detections and controls. However, most past studies had focused on the amplitude responses, not to mention using bi-directional phase responses, in the characterization and light manipulation of chiral metasurfaces. Here, we report a birefringent interference approach to achieve a controllable asymmetric bi-directional transmission phase from planar chiral metasurface by tuning the orientation of the metasurface with respect to the optical axis of an add-on birefringent substrate. To demonstrate our approach, we fabricate planar Au sawtooth nanoarray metasurface and measure the asymmetric transmission phase of the metasurface placed on a birefringent sapphire crystal slab. The Au sawtooth metasurface-sapphire system exhibits large oscillatory behavior for the asymmetric transmission phase with the tuning parameter. We confirm our experimental results by Jones matrix calculations using data obtained from full-wave simulations for the metasurface. Our approach in the characterization and light manipulation of metasurfaces with controllable responses is simple and nondestructive, enabling new functionalities and potential applications in optical communication, imaging, and remote sensing.

In this paper we map the quantum optical scattering of a linear dissipative metasurface to an equivalent Liouvillian dynamics with respect to the effective Hamiltonian of the metasurface propagating in fictitious time. By using a lossy bianisotropic metasurface as a generic example, our formulation allows a complete specification of the generalized eigenspace of the Liouvillian superoperator starting from either a diagonalizable or defective classical scattering matrix of the metasurface. With a further factorization of the Liouvillian superoperator, we demonstrate the input-output relationship on the photon density matrix can be obtained by propagating the photon-moment matrix using a complete basis of the semiclassical Liouvillian superoperator. Our investigations will be useful for characterizing quantum scattering of generally bianisotropic metasurfaces, paving the way for investigating and designing passive parity-time symmetric and non-Hermitian metasurfaces for quantum information processing applications.

By using orthogonal linear-polarized photons, images with tailor-made second-order coherence signatures are generated as “coincidence images” from metasurfaces. The metasurfaces provide arbitrary control on the coincidence signal (correlated, anticorrelated, or uncorrelated photons) at different locations either on the metasurface or the focal plane of the metasurface. The ability to generate polarization coincidence images from metasurfaces is potentially useful for setting up quantum imaging schemes. © 2023, META Conference. All rights reserved.

Qubit operation belonging to unitary transformation is the fundamental operation to realize quantum computing and information processing. Here, we show that the complex and flexible light-matter interaction between dielectric metasurfaces and incident light can be used to perform arbitrary U(2) operations. By incorporating both coherent spatial-mode operation together with two polarizations on a single metasurface, we further extend the discussion to single-photon two-qubit U(4) operations. We believe the efficient usage of metasurfaces as a potential compact platform can simplify optical qubit operation from bulky systems into conceptually subwavelength elements.

Metasurfaces with ultrathin artificial structures have attracted much attention because of their unprecedented capability in light manipulations. The recent development of metasurfaces with controllable responses opens up new opportunities in various applications. Moreover, metasurfaces composed of twisted chiral structures can generate asymmetric responses for opposite incidence, leading to more degrees of freedom in wave detections and controls. However, most past studies had focused on the amplitude responses, not to mention using bi-directional phase responses, in the characterization and light manipulation of chiral metasurfaces. Here, we report a birefringent interference approach to achieve a controllable asymmetric bi-directional transmission phase from planar chiral metasurface by tuning the orientation of the metasurface with respect to the optical axis of an add-on birefringent substrate. To demonstrate our approach, we fabricate planar Au sawtooth nanoarray metasurface and measure the asymmetric transmission phase of the metasurface placed on a birefringent sapphire crystal slab. The Au sawtooth metasurface-sapphire system exhibits large oscillatory behavior for the asymmetric transmission phase with the tuning parameter. We confirm our experimental results by Jones matrix calculations using data obtained from full-wave simulations for the metasurface. Our approach in the characterization and light manipulation of metasurfaces with controllable responses is simple and nondestructive, enabling new functionalities and potential applications in optical communication, imaging, and remote sensing. © 2021 Ranran Zhang et al., published by De Gruyter, Berlin/Boston 2021.

We propose to combine coherent and wavefront control with metasurfaces to carry out designer unitary transformations. The developed framework will be useful for carrying out mathematical operations and quantum information processing. © 2021 META Conference. All rights reserved.

Surface plasmon resonance (SPR) has found wide applications in sensing down to molecular level due to its extreme sensitivity to change of dielectric properties. An unavoidable effect in SPR is surface deformation (thermal bump) due to local heating by incident laser light used in SPR excitation. In addition, the change in reflection phase from an SPR-supported metal film could also contribute to the SPR signal variation, and thus proper handling of measured SPR signals is very important in order to broaden its potential applications. Here a simple Fabry Perot (FP) interference technique for measuring, simultaneously, the thermal bump as well as the reflection phase shift of the gold film used for SPR excitation is reported. The FP signal change is dominated by the appearance of the thermal bump while it is small for the effect of the reflection phase shift due to the change of dielectric property of the metal. To support the experimental results, model simulations for the SPR system are performed and good agreement with the experiment is obtained. The effect of the thermal bump on the resonance of surface plasmon is also investigated and a polarization-dependent reflection phase shift is observed in SPR. Since both amplitude and phase can be measured, our method could lead to a better characterization of SPR and can also be applied to the study of active metasurfaces under external excitation.

Surface plasmon resonance (SPR) has found wide applications in sensing down to molecular level due to its extreme sensitivity to change of dielectric properties. An unavoidable effect in SPR is surface deformation (thermal bump) due to local heating by incident laser light used in SPR. In addition, changes in the reflection phase from the metal film used in SPR could also contribute to the SPR signal, and thus proper handling of the SPR signal is very important in order to broaden the potential applications of SPR. Here we report a simple Fabry Perot (FP) interference technique for measuring, simultaneously, the thermal bump height as well as the reflection phase shift of gold film used in SPR. We find that the shift of the FP signal is dominated by the effect of the thermal bump while it is small for the effect of the reflection phase shift due to change of dielectric property of the metal. To support our experimental results, we have also performed model simulation for the SPR system and obtain good agreement with the experiment. As both amplitude and phase can be measured, our method could lead to better characterization of SPR and can also be applied to the study of active metasurfaces under external excitation.

The studies of photonic crystals had focused on the band structures and complete photonic bandgaps in past decades. However, properties of photonic bands in finite systems are more important for practical applications. Here we report the study of the reflection phase of photonic bands in finite bi-directional 1D dielectric photonic crystal modeled as a dielectric slab using an effective medium with a Fano-like dispersion. The reflection peaks/troughs of the finite photonic crystal slab are analyzed using an interference model to obtain the reflection phase for the photonic bands of the PC. We show that our model works very well in the photonic bands except very close to the band edges. Our work could shed light on practical applications in phase measurements and manipulations using photonic crystals. © 2018 Optical Society of America under the terms of the OSA Open Access Publishing Agreement

We propose a method for the measurement of the reflection phase using a thick-gap Fabry Perot (FP) etalon interferometry technique with correction for the numerical aperture effect of the optical setup. The setup is first calibrated using a known sample by comparing the reflectance from a two-beam interference model for the FP etalon with experimental data. We then apply the correction to a sample of interest and obtain the reflection phase of the sample. Our method can be used to measure the reflection phase of a small sample and could lead to practical applications in optical characterization of metamaterials. Moreover, the principle of our approach could be generalized to other systems in the correction of numerical aperture effect due to microscopic objectives. (C) 2017 Optical Society of America

Metamaterials, artificial materials with sub-wavelength structures capable of exhibiting novel electromagnetic behaviors that could be found in natural materials, have been actively perused as a hot research topic in recent years. The small feature sizes have led to challenges in characterizing the properties of the metamaterials. In this thesis, I aim to develop a technic to measure reflection phase of small samples as the existing methods, such as Ellipsometry, work only for bulk samples. We use a Fabry–Pérot etalon with variable gap-spacing together with a microscope’s objective to obtain reflection interference from areas down to 100 X 100 μm2 in the visible range. We find the reflection interference peaks and troughs shifted by a slowly-varying envelope due to numerical effect of the objective such that the as-measured reflection phase is coupled with the as-measured airgap of the FP etalon. A detailed analysis based on a 2-beams model for the interferogram, with the effect of converging incident beam taken in account, is presented in this work and corrections are applied to the interference peak/trough positions to obtain good agreements with standard values. Furthermore, our method is applied to the measurement of reflection phase of micron-sized Au-sawtooth gratings, demonstrating the potential of our technique in the characterization of small samples.

We report measurement of the reflection phase of a dielectric (glass)/titanium (Ti) surface in the visible wavelength using a thick-gap Fabry-Perot (FP) interferometry technique. Using a two-beam interference model for the reflection peaks and troughs of the FP etalon, we obtain the air-gap spacing of the etalon and, more importantly, the reflection phase of the etalon substrate. We find systematic dependence of the as-measured reflection phase on the air-gap spacing due to the numerical aperture effect of the measuring objective. However, the relative reflection phase of Ti with respect to glass is independent of the air-gap spacing. As a demonstration of our approach in the optical characterization of small metamaterial samples, we also measure the reflection phase of a micron-sized 2D Au sawtooth nanoarray. The experiment is in good agreement with the model simulation. © 2016 Optical Society of America.

We report measurement of the reflection phase of a dielectric (glass)/titanium (Ti) surface in the visible wavelength using a thick-gap Fabry-Perot (FP) interferometry technique. Using a two-beam interference model for the reflection peaks and troughs of the FP etalon, we obtain the air-gap spacing of the etalon and, more importantly, the reflection phase of the etalon substrate. We find systematic dependence of the as-measured reflection phase on the air-gap spacing due to the numerical aperture effect of the measuring objective. However, the relative reflection phase of Ti with respect to glass is independent of the air-gap spacing. As a demonstration of our approach in the optical characterization of small metamaterial samples, we also measure the reflection phase of a micron-sized 2D Au sawtooth nanoarray. The experiment is in good agreement with the model simulation.