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Conference on Lasers and Electro-Optics Europe & European Quantum Electronics Conference (CLEO/Europe-EQEC)

Coherent absorption of two-photon states in metamaterials

Thomas Roger, Ashley Lyons, Dikla Oren, Vassili Savinov, João Valente, Stefano Vezzoli, Mordechai Segev, Nikolay I. Zheludev, Daniele Faccio

Published Jun 1, 2017• 0 citations
Publisher

Abstract

Multiple photon absorption processes typically have a nonlinear dependence on the amplitude of the incident optical field. On the other hand, quantum technologies rely on single photon events. It has therefore been of great technical difficulty to achieve nonlinear devices using single photons. This is due to the small cross-section of absorption in room temperature devices, with multi-photon absorption events occurring with extremely low probability. The lack of access to nonlinear processes severely inhibits the use of optics for a large number of applications surrounding quantum technologies. We demonstrate experimentally that by exploiting a coherent absorption mechanism for N=2 N00N states, outlined theoretically by Jeffers in 2000 [1] and experimentally explored by Roger et. al. in 2016 [2], that it is possible to determine and enhance the number of two photon states that are absorbed. Here a 50% absorbing metasurface is placed inside a Sagnac interferometer into which we inject a N00N state. We show that by tuning the phase φ of the input state, |2,0〉 + exp(-ί2φ) |0,2〉, we can selectively tune the output state. For an input phase of φ = π/2 or 3π/2 we find that a single photon is absorbed with 100% probability. However, when we tune the input phase to φ = 0 or π we see that either 0 or 2 photons are absorbed with equal probability. We have developed a theoretical model that, with no free parameters, fits the experimentally measured two-photon contribution and finds the maximum contribution of |0,0) (0,0| to the output state to be 40.5%.

DOI
10.1109/cleoe-eqec.2017.8087659

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Multiple photon absorption processes typically have a nonlinear dependence on the amplitude of the incident optical field. On the other hand, quantum technologies rely on single photon events. It has therefore been of great technical difficulty to achieve nonlinear devices using single photons. This is due to the small cross-section of absorption in room temperature devices, with multi-photon absorption events occurring with extremely low probability. The lack of access to nonlinear processes severely inhibits the use of optics for a large number of applications surrounding quantum technologies. We demonstrate experimentally that by exploiting a coherent absorption mechanism for N=2 N00N states, outlined theoretically by Jeffers in 2000 [1] and experimentally explored by Roger et. al. in 2016 [2], that it is possible to determine and enhance the number of two photon states that are absorbed. Here a 50% absorbing metasurface is placed inside a Sagnac interferometer into which we inject a N00N state. We show that by tuning the phase φ of the input state, |2,0〉 + exp(-ί2φ) |0,2〉, we can selectively tune the output state. For an input phase of φ = π/2 or 3π/2 we find that a single photon is absorbed with 100% probability. However, when we tune the input phase to φ = 0 or π we see that either 0 or 2 photons are absorbed with equal probability. We have developed a theoretical model that, with no free parameters, fits the experimentally measured two-photon contribution and finds the maximum contribution of |0,0) (0,0| to the output state to be 40.5%.
Multiphoton absorption processes have a nonlinear dependence on the amplitude of the incident optical field, i.e., the number of photons. However, multiphoton absorption is generally weak and multiphoton events occur with extremely low probability. Consequently, it is extremely challenging to engineer quantum nonlinear devices that operate at the single photon level and the majority of quantum technologies have to rely on single photon interactions. Here we demonstrate experimentally and theoretically that exploiting coherent absorption of N=2N=2N=2 NOON states makes it possible to enhance the number of two-photon states that are absorbed by at most a factor of 2 with respect to a linear absorption process. An absorbing metasurface placed inside a Sagnac-style interferometer into which we inject an N=2N=2N=2 NOON state, exhibits two-photon absorption with 40.540.5%40.5 efficiency, close to the theoretical maximum. This high probability of simultaneous absorption of two photons holds the promise for applications in fields that require multiphoton upconversion but are hindered by high peak intensities.
Recent results in deeply subwavelength thickness films demonstrate coherent control and logical gate operations with both classical and single-photon light sources. However, quantum processing and devices typically involve more than one photon and nontrivial input quantum states. Here we experimentally investigate two-photon N00N state coherent absorption in a multilayer graphene film. Depending on the N00N state input phase, it is possible to selectively choose between single- or two-photon absorption of the input state in the graphene film. These results demonstrate that coherent absorption in the quantum regime exhibits unique features, opening up applications in multiphoton spectroscopy and imaging.
Multiphoton absorption is of vital importance in many spectroscopic, microscopic, or lithographic applications. However, given that it is an inherently weak process, the detection of multiphoton absorption signals typically requires large field intensities, hindering its applicability in many practical situations. In this Letter, we show that placing a multiphoton absorbent inside an imbalanced nonlinear interferometer can enhance the precision of multiphoton cross section estimation with respect to strategies based on photon-number measurements using coherent or even squeezed light directly transmitted through the medium. In particular, the power scaling of the sensitivity with photon flux can be increased by 1 order compared with transmission measurements of the sample with coherent light, such that the measurement precision at any given intensity can be greatly enhanced. Furthermore, we show that this enhanced measurement precision is robust against experimental imperfections leading to photon losses, which usually tend to degrade the detection sensitivity. We trace the origin of this enhancement to an optimal degree of squeezing which has to be generated in a nonlinear SU(1,1) interferometer.
Reverse saturable absorption (RSA) occurs in nonlinear materials where the excited state exhibits higher absorption than the ground state. This study presents a full-wave spatio-temporal numerical model that accurately simulates coherent RSA by coupling quantum systems with Maxwell’s equations. The model enables the design of complex photonic metamaterials and metasurfaces beyond the capabilities of conventional absorption models. To demonstrate its effectiveness, we analyze a metasurface-enhanced optical absorber, achieving over twice the absorption enhancement compare to the bare layer. This approach paves the way for highly efficient low-power optical absorption devices, with applications in protective optics and photonic elements.
Interferometers provide a highly sensitive means to investigate and exploit the coherence properties of light in metrology applications. However, interferometers come in various forms and exploit different properties of the optical states within. In this paper, we introduce a classification scheme that characterizes any interferometer based on the number of involved nonlinear elements by studying their influence on single-photon and photon-pair states. Several examples of specific interferometers from these more general classes are discussed, and the theory describing the expected first-order and second-order coherence measurements for single-photon and single-photon-pair input states is summarized and compared. These theoretical predictions are then tested in an innovative experimental setup that is easily able to switch between implementing an interferometer consisting of only one or two nonlinear elements. The resulting singles and coincidence rates are measured in both configurations and the results are seen to fit well with the presented theory. The measured results of coherence are tied back to the presented classification scheme, revealing that our experimental design can be useful in gaining insight into the properties of the various interferometeric setups containing different degrees of nonlinearity.
The absorption of a single photon that excites a quantum system from a low to a high energy level is an elementary process of light-matter interaction, and a route towards realizing pure single-photon absorption has both fundamental and practical implications in quantum technology. Due to nonlinear optical effects, however, the probability of pure single-photon absorption is usually very low, which is particularly pertinent in the case of strong ultrafast laser pulses with broad bandwidth. Here we demonstrate theoretically a counterintuitive coherent single-photon absorption scheme by eliminating nonlinear interactions of ultrafast laser pulses with quantum systems. That is, a completely linear response of the system with respect to the spectral energy density of the incident light at the transition frequency can be obtained for all transition probabilities between 0 and 100% in multilevel quantum systems. To that end, a multiobjective optimization algorithm is developed to find an optimal spectral phase of an ultrafast laser pulse, which is capable of eliminating all possible nonlinear optical responses while maximizing the probability of single-photon absorption between quantum states. This work not only deepens our understanding of light-matter interactions, but also offers a way to study photophysical and photochemical processes in the ``absence'' of nonlinear optical effects.