Single-photon Coupling Research Articles

Direct observation of a few-photon phase shift induced by a single quantum emitter in a waveguide

Realizing a sensitive photon-number-dependent phase shift on a light beam is required both in classical and quantum photonics. It may lead to new applications for classical and quantum photonics machine learning or pave the way for realizing photon-photon gate operations. Nonlinear phase-shifts require efficient light-matter interaction, and recently quantum dots coupled to nanophotonic devices have enabled near-deterministic single-photon coupling. We experimentally realize an optical phase shift of 0.19π ± 0.03 radians ( ≈ 34 degrees) using a weak coherent state interacting with a single quantum dot in a planar nanophotonic waveguide. The phase shift is probed by interferometric measurements of the light scattered from the quantum dot in the waveguide. The process is nonlinear in power, the saturation at the single-photon level and compatible with scalable photonic integrated circuitry. The work may open new prospects for realizing high-efficiency optical switching or be applied for proof-of-concept quantum machine learning or quantum simulation demonstrations.

Single-photon induced instabilities in a cavity electromechanical device

Cavity-electromechanical systems are extensively used for sensing and controlling the vibrations of mechanical resonators down to their quantum limit. The nonlinear radiation-pressure interaction in these systems could result in an unstable response of the mechanical resonator showing features such as frequency-combs, period-doubling bifurcations and chaos. However, due to weak light-matter interaction, typically these effects appear at very high driving strengths. By using polariton modes formed by a strongly coupled flux-tunable transmon and a microwave cavity, here we demonstrate an electromechanical device and achieve a single-photon coupling rate g0/2π\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\left({g}_{0}/2\\pi \\right)$$\\end{document} of 160 kHz, which is nearly 4% of the mechanical frequency ωm. Due to large g0/ωm ratio, the device shows an unstable mechanical response resulting in frequency combs in sub-single photon limit. We systematically investigate the boundary of the unstable response and identify two important regimes governed by the optomechanical backaction and the nonlinearity of the electromagnetic mode. Such an improvement in the single-photon coupling rate and the observations of microwave frequency combs at single-photon levels may have applications in the quantum control of the motional states and critical parametric sensing. Our experiments strongly suggest the requirement of newer approaches to understand instabilities.

Simulation of optomechanical interaction of levitated nanoparticle with photonic crystal micro cavity.

We propose and analyze theoretically a promising design of an optical trap for vacuum levitation of nanoparticles based on a one-dimensional (1D) silicon photonic crystal cavity (PhC). The considered cavity has a quadratically modulated width of the silicon wave guiding structure, leading to a calculated cavity quality factor of 8 × 105. An effective mode volume of approximately 0.16 μm3 having the optical field strongly confined outside the silicon structure enables optical confinement on nanoparticle in all three dimensions. The optical forces and particle-cavity optomechanical coupling are comprehensively analyzed for two sizes of silica nanoparticles (100 nm and 150 nm in diameter) and various mode detunings. The value of trapping stiffnesses in the microcavity is predicted to be 5 order of magnitudes higher than that reached for optimized optical tweezers, moreover the linear single photon coupling rate can reach MHz level which is 6 order magnitude larger than previously reported values for common bulk cavities. The theoretical results support optimistic prospects towards a compact chip for optical levitation in vacuum and cooling of translational mechanical degrees of motion for the silica nanoparticle of a diameter of 100 nm.

Slot waveguide enhanced asymmetric photonic crystal nanofiber cavity for fiber-coupled single photons

We report a slot waveguide-enhanced asymmetric photonic crystal optical nanofiber (ONF) cavity to realize cavity quantum electrodynamics. We show that the device can strongly enhance the spontaneous emission of a single quantum emitter leading to a Purcell factor as high as 106 and enables single-photon coupling efficiency as high as 86% into fiber-guided modes. The introduction of the slot enhances the Purcell factor by six times as compared to the ONF cavity structure without slot, and the asymmetric cavity design enables unidirectional coupling of single photons. The cavity is designed to minimize the losses leading to a scattering-limited Q-factor and one-pass loss estimated to be 6388 and 1.2%, respectively. This fiber-coupled single-photon device may open advanced possibilities and applications for quantum information processing.

Terahertz phononic crystal in plasmonic nanocavity

Interaction between photons and phonons in cavity optomechanical systems provides a new toolbox for quantum information technologies. A GaAs/AlAs pillar multi-optical mode microcavity optomechanical structure can obtain phonons with ultra-high frequency (~THz). However, the optical field cannot be effectively restricted when the diameter of the GaAs/AlAs pillar microcavity decreases below the diffraction limit of light. Here, we design a system that combines Ag nanocavity with GaAs/AlAs phononic superlattices, where phonons with the frequency of 4.2 THz can be confined in a pillar with ~4 nm diameter. The Q c/V reaches 0.22 nm−3, which is ~80 times that of the photonic crystal (PhC) nanobeam and ~100 times that of the hybrid point-defect PhC bowtie plasmonic nanocavity, where Q c is optical quality factor and V is mode volume. The optomechanical single-photon coupling strength can reach 12 MHz, which is an order of magnitude larger than that of the PhC nanobeam. In addition, the mechanical zero-point fluctuation amplitude is 85 fm and the efficient mass is 0.27 zg, which is much smaller than the PhC nanobeam. The phononic superlattice-Ag nanocavity optomechanical devices hold great potential for applications in the field of integrated quantum optomechanics, quantum information, and terahertz-light transducer.

Photonic transistor based on a coupled-cavity system with polaritons.

We investigate the transmission of probe fields in a coupled-cavity system with polaritons and propose a theoretical schema for realizing a polariton-based photonic transistor. When probe light passes through such a hybrid optomechanical device, its resonant point with Stokes or anti-Stokes scattered effects, intensity with amplification or attenuation effects, as well as group velocity with slow or fast light effects can be effectively controlled by another pump light. This controlling depends on the exciton-photon coupling and single-photon coupling. We also discover an asymmetric Fano resonance in transparency windows under the strong exciton-photon coupling, which is different from general symmetric optomechanically induced transparency. Our results open up exciting possibilities for designing photonic transistors, which may be useful for implementing polariton integrated circuits.

Radiation Pressure Backaction on a Hexagonal Boron Nitride Nanomechanical Resonator.

Hexagonal boron nitride (hBN) is a van der Waals material with excellent mechanical properties hosting quantum emitters and optically active spin defects, with several of them being sensitive to strain. Establishing optomechanical control of hBN will enable hybrid quantum devices that combine the spin degree of freedom with the cavity optomechanical toolbox. In this Letter, we report the first observation of radiation pressure backaction at telecom wavelengths with a hBN drum-head mechanical resonator. The thermomechanical motion of the resonator is coupled to the optical mode of a high finesse fiber-based Fabry-Pérot microcavity in a membrane-in-the-middle configuration. We are able to resolve the optical spring effect and optomechanical damping with a single photon coupling strength of g0/2π = 1200 Hz. Our results pave the way for tailoring the mechanical properties of hBN resonators with light.

A novel architecture for room temperature microwave optomechanical experiments

We have developed a novel architecture for room temperature microwave cavity optomechanics, which is based on the coupling of a 3D microwave re-entrant cavity to a compliant membrane. Device parameters have enabled resolving the thermomechanical motion of the membrane and observing optomechanically induced transparency/absorption in the linear regime for the first time in a microwave optomechanical system operated at room temperature. We have extracted the single-photon coupling rate (g0) using four independent measurement techniques and, hence, obtained a full characterization of the proposed cavity optomechanical system.

Enhanced sensing of optomechanically induced nonlinearity by linewidth suppression and optical bistability in cavity-waveguide systems.

We study the enhanced sensing of optomechanically induced nonlinearity (OMIN) in a cavity-waveguide coupled system. The Hamiltonian of the system is anti-PT symmetric, with the two involved cavities being dissipatively coupled via the waveguide. The anti-PT symmetry may break down when a weak waveguide-mediated coherent coupling is introduced. However, we find a strong bistable response of the cavity intensity to the OMIN near the cavity resonance, benefiting from linewidth suppression caused by the vacuum induced coherence. The joint effect of optical bistability and the linewidth suppression is inaccessible by the anti-PT symmetric system involving only dissipative coupling. Due to that, the sensitivity measured by an enhancement factor is greatly enhanced by two orders of magnitude compared to that for the anti-PT symmetric model. Moreover, the enhancement factor shows resistance to a reasonably large cavity decay and robustness to fluctuations in the cavity-waveguide detuning. Based on the integrated optomechanical cavity-waveguide systems, the scheme can be used for sensing different physical quantities related to the single-photon coupling strength and has potential applications in high-precision measurements with systems involving Kerr-type nonlinearity.

Detection of HCl molecules by resonantly enhanced sum-frequency mixing of mid- and near-infrared laser pulses

We perform experimental studies of resonantly enhanced sum-frequency mixing (SFM), driven by tunable, spectrally narrowband mid-infrared and fixed-frequency nanosecond laser pulses, aiming at applications in molecular gas detection. The mid-infrared pulses are tuned in the vicinity of two-photon rovibrational transitions in the electronic ground state to provide strong resonance enhancements of the nonlinear susceptibility, while a probe laser at shorter wavelength uses an off-resonant single-photon coupling to excited electronic states. This SFM approach benefits from the advantageous combination of typically small detunings among the mid-infrared, vibrational transitions and the typically large transition dipole moment for couplings of electronic states. Moreover, compared to resonantly enhanced third harmonic generation (THG), a signal wave at much shorter wavelength permits simple and efficient detection. We demonstrate resonantly enhanced SFM via rovibrational states in gaseous hydrogen chloride molecules and compare its features to THG. The SFM spectra offer a large signal-to-noise ratio of 4 orders of magnitude and a detection limit down to a pressure of 0.1 mbar, corresponding to a particle density of $0.35\ifmmode\times\else\texttimes\fi{}{10}^{15}$ per ${\mathrm{cm}}^{3}$.

Silicon Nitride Waveguides with Intrinsic Single-Photon Emitters for Integrated Quantum Photonics

The recent discovery of room temperature intrinsic single-photon emitters in silicon nitride (SiN) provides the unique opportunity for seamless monolithic integration of quantum light sources with the well-established SiN photonic platform. In this work, we develop a novel approach to realize planar waveguides made of low-autofluorescing SiN with intrinsic quantum emitters and demonstrate the single-photon emission coupling into the waveguide mode. The observed emission coupling from these emitters is found to be in line with numerical simulations. The coupling of the single-photon emission to a waveguide mode is confirmed by second-order autocorrelation measurements of light outcoupled off the photonic chip by grating couplers. Fitting the second-order autocorrelation histogram yields $g^{(2)}(0)=0.35\pm0.12$ without spectral filtering or background correction with an outcoupled photon rate of $10^4$ counts per second. This demonstrates the first successful coupling of photons from intrinsic single-photon emitters in SiN to monolithically integrated waveguides made of the same material. The results of our work pave the way toward the realization of scalable, technology-ready quantum photonic integrated circuitry efficiently interfaced with solid-state quantum emitters.

Large-bandwidth Transduction Between an Optical Single Quantum Dot Molecule and a Superconducting Resonator

Quantum transduction between the microwave and optical domains is an outstanding challenge for long-distance quantum networks based on superconducting qubits. For all transducers realized to date, the generally weak light-matter coupling does not allow high transduction efficiency, large bandwidth, and low noise simultaneously. Here we show that a large electric dipole moment of an exciton in an optically active self-assembled quantum dot molecule (QDM) efficiently couples to a microwave resonator field at a single-photon level. This allows for transduction between microwave and optical photons without coherent optical pump fields to enhance the interaction. With an on-chip device, we demonstrate a sizeable single-photon coupling strength of 16 MHz. Thanks to the fast exciton decay rate in the QDM, the transduction bandwidth between an optical and microwave resonator photon reaches several 100s of MHz.

Parametrically enhanced interactions and nonreciprocal bath dynamics in a photon-pressure Kerr amplifier.

Photon-pressure coupling between two superconducting circuits is a promising platform for investigating radiation-pressure coupling in distinct parameter regimes and for the development of radio-frequency (RF) quantum photonics and quantum-limited RF sensing. Here, we implement photon-pressure coupling between two superconducting circuits, one of which can be operated as a parametric amplifier. We demonstrate a Kerr-based enhancement of the photon-pressure single-photon coupling rate and an increase of the cooperativity by one order of magnitude in the amplifier regime. In addition, we observe that the intracavity amplification reduces the measurement imprecision of RF signal detection. Last, we demonstrate that RF mode sideband cooling is unexpectedly not limited to the effective amplifier mode temperature arising from quantum noise amplification, which we interpret in the context of nonreciprocal heat transfer between the two circuits. Our results demonstrate how Kerr amplification can be used as resource for enhanced photon-pressure systems and Kerr cavity optomechanics.

Optomagnonics in Dispersive Media: Magnon-Photon Coupling Enhancement at the Epsilon-near-Zero Frequency.

Reaching strong light-matter coupling in solid-state systems has long been pursued for the implementation of scalable quantum devices. Here, we put forward a system based on a magnetized epsilon-near-zero (ENZ) medium, and we show that strong coupling between magnetic excitations (magnons) and light can be achieved close to the ENZ frequency due to a drastic enhancement of the magneto-optical response. We adopt a phenomenological approach to quantize the electromagnetic field inside a dispersive magnetic medium in order to obtain the frequency-dependent coupling between magnons and photons. We predict that, in the epsilon-near-zero regime, the single-magnon single-photon coupling can be comparable to the magnon frequency for a small magnetic volume and perfect mode overlap. For state-of-the-art illustrative values, this would correspond to achieving the single-magnon strong coupling regime, where the coupling rate is larger than all the decay rates. Finally, we show that the nonlinear energy spectrum intrinsic to this coupling regime can be probed via the characteristic multiple magnon sidebands in the photon power spectrum.

Twin-nanofiber structure for a highly efficient single-photon collection.

Optical nanofiber-based single-photon source has attracted considerable interest due to its property of seamless integration with a single-mode fiber. With nanostructure engraved in the nanofiber, the single-photon collection efficiency can be greatly boosted with enhanced interaction between the single quantum emitter and the guided light. However, the prerequisite nanofabrication processes introduce complexities and extra loss. Here, we demonstrate that by simply placing a quantum emitter in the gap of two parallel nanofibers, single-photon coupling efficiency may reach 54.2%. Our numerical simulation results indicate that photon coupling efficiency of such simple structure is insensitive to the discrepancy in nanofiber radii, which further reduces the difficulties in device fabrication.

Four-wave-cooling to the single phonon level in Kerr optomechanics

Cavity optomechanics has achieved groundbreaking control and detection of mechanical oscillators, based on their coupling to linear electromagnetic modes. Recently, however, there is increasing interest in cavity nonlinearities as resource in radiation-pressure interacting systems. Here, we present a flux-mediated optomechanical device combining a nonlinear superconducting quantum interference cavity with a mechanical nanobeam. We demonstrate how the Kerr nonlinearity of the circuit can be used to enhance the device performance by suppressing cavity frequency noise, and for a counter-intuitive sideband-cooling scheme based on intracavity four-wave-mixing. With a large single-photon coupling rate of up to g0 = 2π ⋅ 3.6 kHz and a high mechanical quality factor Qm ≈ 4 ⋅ 105, we achieve an effective four-wave cooperativity of {{{{{{{{mathcal{C}}}}}}}}}_{{{{{{{{rm{fw}}}}}}}}}, > , 100 and demonstrate four-wave cooling of the mechanical oscillator close to its quantum groundstate. Our results advance the recently developed platform of flux-mediated optomechanics and demonstrate how cavity Kerr nonlinearities can be utilized in cavity optomechanics.

Optomechanical strong coupling between a single photon and a single atom

Single atoms coupled to a cavity offer unique opportunities as quantum optomechanical devices because of their small mass and strong interaction with light. A particular regime of interest in optomechanics is that of ‘single-photon strong coupling’, where motional displacements on the order of the zero-point uncertainty are sufficient to shift the cavity resonance frequency by more than its linewidth. In many cavity QED platforms, however, this is unfeasible due to the large cavity linewidth. Here, we propose an alternative route in such systems, which instead relies on the coupling of atomic motion to the much narrower cavity-dressed atomic resonance frequency. We discuss and optimize the conditions in which the scattering properties of single photons from the atom-cavity system become highly entangled with the atomic motional wave function. We also analyze the prominent observable features of this optomechanical strong coupling, which include a per-photon motional heating that is significantly larger than the single-photon recoil energy, as well as mechanically-induced oscillations in time of the second-order correlation function of the emitted light. This physics should be realizable in current experimental setups, such as trapped atoms coupled to photonic crystal cavities, and more broadly opens the door to realizing qualitatively different phenomena beyond what has been observed in optomechanical systems thus far.

Fast and Ultrasensitive Electrometer Operating at the Single-Photon Level

We demonstrate fast and ultrasensitive charge detection with a cavity-embedded Cooper pair transistor (cCPT) via dispersive readout of its Josephson inductance. We report a minimum charge sensitivity of $14$ $\mu e/\sqrt{\mathrm{Hz}}$ with a detection bandwidth on the order of $1$ MHz using $16$ attowatts of power, corresponding to the single-photon level of the cavity. In addition, our measured sensitivities are within a factor of $5$ of the quantum limit for this device. The single-photon-level sensitivity of the cCPT is comparable to that of the rf-SET, which typically operates using picowatts of power corresponding to hundreds of thousands of photons in its tank circuit. Our results support the feasibility of using the cCPT to mediate an optomechanical interaction that reaches the single-photon strong coupling regime.

Engineering Long-Lived Vibrational States for an Organic Molecule.

The optomechanical character of molecules was discovered by Raman about one century ago. Today, molecules are promising contenders for high-performance quantum optomechanical platforms because their small size and large energy-level separations make them intrinsically robust against thermal agitations. Moreover, the precision and throughput of chemical synthesis can ensure a viable route to quantum technological applications. The challenge, however, is that the coupling of molecular vibrations to environmental phonons limits their coherence to picosecond time scales. Here, we improve the optomechanical quality of a molecule by several orders of magnitude through phononic engineering of its surrounding. By dressing a molecule with long-lived high-frequency phonon modes of its nanoscopic environment, we achieve storage and retrieval of photons at millisecond timescales and allow for the emergence of single-photon strong coupling in optomechanics. Our strategy can be extended to the realization of molecular optomechanical networks.

Suppressing laser phase noise in an optomechanical system

We propose a scheme to suppress the laser phase noise without increasing the optomechanical single-photon coupling strength. In the scheme, the parametric amplification terms, created by Kerr and Duffing nonlinearities, can restrain laser phase noise and strengthen the effective optomechanical coupling, respectively. Interestingly, decreasing laser phase noise leads to increasing thermal noise, which is inhibited by bringing in a broadband-squeezed vacuum environment. To reflect the superiority of the scheme, we simulate quantum memory and stationary optomechanical entanglement as examples, and the corresponding numerical results demonstrate that the laser phase noise is extremely suppressed. Our method can pave the way for studying other quantum phenomena.