High-Visibility On-Chip Quantum Interference of Single Surface Plasmons

Abstract

Quantum photonic integrated circuits (QPICs) based on dielectric waveguides have been widely used in linear optical quantum computation. Recently, surface plasmons have been introduced to this application because they can confine and manipulate light beyond the diffraction limit. In this study, the on-chip quantum interference of two single surface plasmons was achieved using dielectric-loaded surface-plasmon-polariton waveguides. The high visibility (greater than 90%) proves the bosonic nature of single plasmons and emphasizes the feasibility of achieving basic quantum logic gates for linear optical quantum computation. The effect of intrinsic losses in plasmonic waveguides with regard to quantum information processing is also discussed. Although the influence of this effect was negligible in the current experiment, our studies reveal that such losses can dramatically reduce quantum interference visibility in certain cases; thus, quantum coherence must be carefully considered when designing QPIC devices.Photonic integrated circuits (PICs), in which multiple photonic functional components comprise a single chip, have attracted considerable attention owing to their small footprints, scalability, reduced power consumption, and enhanced processing stability. In addition to their wide application in classical information processing, integrated photonic quantum logic gates and Shor's quantum factoring algorithm have been demonstrated on these chips [1, 2]; thus, they show great feasibility and high operation fidelity. More recently, much effort has been dedicated to surface plasmon polaritons (SPPs), which are electron density waves excited at the interface between a metal and a dielectric material [3]to further condense PICs beyond the diffraction limit. Not only can SPPs confine light at the nanoscale [4], they are also useful for integrated polarization-controlling devices [5,6]. Studies using periodic metallic hole arrays provided the first experimental evidence that quantum entanglement can be preserved in the photon-SPP-photon conversion process [7][8][9]. Furthermore, the nonclassical statistics of SPPs have been demonstrated using basic quantum Hong-Ou-Mandel (HOM) interference [10], in both long-range plasmonic waveguides (weakly confining waveguide) [11] and sub-wavelength metal plasmonic waveguides [12]. These studies indicate that assembling quantum PICs (QPICs) using plasmonic components is possible.However, two obstacles remain that hinder the development of SPP-based QPICs. The first is that the experimental raw visibility of the quantum interference realized in plasmonic waveguides is below 50% [12], which is the boundary between classical and quantum interference. This low visibility is not compelling evidence that single plasmons are usable for quantum information processing. Interference visibility is so important that higher quantum interference visibility implies higher operation fidelity and a higher probability of success. For example, the HOM interference with 95% visibility * renxf@ustc.edu.c...

Quantum Plasmonics

“…In fact it has been experimentally demonstrated that SPPs exhibit single particle statistics [1], [34], [57], [73]. Recently, there have been some remarkable experiments that have shown quantum interference between SPPs [22], [35], [45], [49], [58] in particular by performing a plasmonic version of the Hong-Ou-Mandel effect [61]. An example of this iconic quantum optics experiment is represented in fig 5 [35].…”

Highly Efficient Excitation of Surface Plasmons Using a Si Gable Tip

“…The proposed gabled Si tip SPP excitation scheme can also be useful in enhanced nonlinear applications . Furthermore, such highly efficient SPP excitation technique can be useful for an easier and compact excitation of SPPs for experiments studying quantum properties of surface plasmon polaritons …”

Transmission of entangled photons studied by quantum tomography: do we need plasmonic resonances?

“…The work of Olislager et al [2] reviewed different quantum experiments with plasmons, such as Young's double-slit experiment [9], evidence of quantum superpositions of single plasmons [10][11][12][13][14], and the generation of plasmonic squeezed states [15], as well as two-particle experiments [16][17][18][19][20][21]. The studies mentioned above proved the quantum bosonic nature of plasmonic excitations.…”