Storing single photons emitted by a quantum memory on a highly excited Rydberg state

Strongly Nonlinear Interaction between Nonclassical Light and a Blockaded Rydberg Atomic Ensemble

We investigate the interaction between nonclassical light with a tunable multiphoton component and a highly nonlinear medium based on cold Rydberg atoms. The nonclassical field emitted by a DLCZ quantum memory is stored using Rydberg electromagnetically induced transparency, experiencing strong nonlinear response due to the dipole blockade. We show that the storage efficiency in the Rydberg ensemble decreases as a function of the multiphoton strength of the input field, as a result of the nonlinearity. We also show that the autocorrelation function g^{(2)}(0) of the retrieved field after storage in the Rydberg state is considerably reduced, leading to the first demonstration of single photon filtering with nonclassical input light. Finally, we develop a simple simulation that allows us to model the effect of our medium on the input state. This work is a step towards matter-mediated photon-photon interactions with nonclassical light.

Touchless Input/Output Interface for Device-to-Device Communication

Multiple quantum well (MQW) III-nitride diodes show selectable functionalities of light-emitting and light-detecting behaviors, enabling direct touchless device-to-device communication. Here, we propose and demonstrate a touchless input/output (I/O) interface using a single MQW III-nitride diode. By integrating an MQW III-nitride diode with a memory via a control circuit, optical signals are converted into electrical ones to be written into a memory, and consequently, electrical information is read out from the memory to be translated into optical signals for visible light communication (VLC). The MQW III-nitride diode can not only lead to a touchless ″writing″ action but also offer a ″reading″ process through light. Such touchless I/O interface would provide new forms of interactivity for device-to-device communication technologies.

Tailoring dual-band electromagnetically induced transparency with polarization conversions in a dielectric-metal hybrid metastructure

Metastructure analogs of electromagnetically induced transparency (EIT) provide a new approach for engineering realizations of nonlinear optical manipulations regardless of harsh conditions; further can be employed in polarization conversions for its low-loss transmission and phase modulation. In this work, dual-band EIT in a dielectric-metal hybrid metasurface achieved via providing different coupling channels is theoretically investigated with a maximum group delay of 404 ps. The linear-to-circular polarization conversion (LCPC) behaviors are observed respectively holding the transmittance of 0.58 at 0.68 THz, 0.73 at 0.76 THz, 0.61 at 0.90 THz, 0.53 at 0.99 THz, owning to the asymmetric EIT responses in the transverse magnetic (TM) and transverse electric (TE) modes incidence. On the other hand, phase-transition VO₂ is doped to perturb the dark mode resonances. With its conductivity σ = 10⁵ S/m, dual transparency peaks transform into unimodal broadband transmission windows with relative bandwidths of 17.1% and 9.1% under the TE and TM excitations apart. Induced LCPC possesses a bandwidth of 10.4% centered at 0.76 THz attributed to the drastic dispersion. The as-proposed design exploits pattern asymmetry of EIT responses to realize LCPC, promising the wide prospect of reconfigurable multiplexings.

Quantum Nonlinear Optics Based on Two-Dimensional Rydberg Atom Arrays

We propose the combination of subwavelength, two-dimensional atomic arrays and Rydberg interactions as a powerful platform to realize strong, coherent interactions between individual photons with high fidelity. The atomic spatial ordering guarantees efficient atom-light interactions without the possibility of scattering light into unwanted directions, allowing the array to act as a perfect mirror for individual photons. In turn, Rydberg interactions enable single photons to alter the optical response of the array within a potentially large blockade radius R_{b}, which can effectively punch a large "hole" for subsequent photons. We show that such a system enables a coherent photon-photon gate or switch, with a significantly better error scaling (∼R_{b}^{-4}) than in a disordered ensemble. We also investigate the optical properties of the system in the limit of strong input intensities and show that this many-body quantum driven dissipative system can be modeled well by a semiclassical model based on holes punched in a classical mirror.

Autoheterodyne Characterization of Narrow-Band Photon Pairs

We describe a technique to measure photon pair joint spectra by detecting the time-correlation beat note when nondegenerate photon pairs interfere at a beam splitter. The technique implements a temporal analog of the Ghosh-Mandel effect with one photon counter and a time-resolved Hong-Ou-Mandel interference with two. It is well suited to characterize pairs of photons, each of which can interact with a single atomic species, as required to study recently predicted photon-photon interaction in subwavelength atomic arrays. With this technique, we characterize photon pairs from cavity-enhanced parametric down-conversion with a bandwidth ≈ 5  MHz and frequency separation of ∼200  MHz near the D_{1} line of atomic Rb.

Controlled multi-photon subtraction with cascaded Rydberg superatoms as single-photon absorbers

The preparation of light pulses with well-defined quantum properties requires precise control at the individual photon level. Here, we demonstrate exact and controlled multi-photon subtraction from incoming light pulses. We employ a cascaded system of tightly confined cold atom ensembles with strong, collectively enhanced coupling of photons to Rydberg states. The excitation blockade resulting from interactions between Rydberg atoms limits photon absorption to one per ensemble and rapid dephasing of the collective excitation suppresses stimulated re-emission of the photon. We experimentally demonstrate subtraction with up to three absorbers. Furthermore, we present a thorough theoretical analysis of our scheme where we identify weak Raman decay of the long-lived Rydberg state as the main source of infidelity in the subtracted photon number and investigate the performance of the multi-photon subtractor for increasing absorber numbers in the presence of Raman decay.

Interaction of photons with Rydberg atoms can be used to modify quantum states of light. Here the authors demonstrate a controlled nonlinear quantum behavior of multi-photon subtraction in a cascaded system based on Rydberg superatoms.

Optimizing High-Efficiency Quantum Memory with Quantum Machine Learning for Near-Term Quantum Devices

Quantum memories are a fundamental of any global-scale quantum Internet, high-performance quantum networking and near-term quantum computers. A main problem of quantum memories is the low retrieval efficiency of the quantum systems from the quantum registers of the quantum memory. Here, we define a novel quantum memory called high-retrieval-efficiency (HRE) quantum memory for near-term quantum devices. An HRE quantum memory unit integrates local unitary operations on its hardware level for the optimization of the readout procedure and utilizes the advanced techniques of quantum machine learning. We define the integrated unitary operations of an HRE quantum memory, prove the learning procedure, and evaluate the achievable output signal-to-noise ratio values. We prove that the local unitaries of an HRE quantum memory achieve the optimization of the readout procedure in an unsupervised manner without the use of any labeled data or training sequences. We show that the readout procedure of an HRE quantum memory is realized in a completely blind manner without any information about the input quantum system or about the unknown quantum operation of the quantum register. We evaluate the retrieval efficiency of an HRE quantum memory and the output SNR (signal-to-noise ratio). The results are particularly convenient for gate-model quantum computers and the near-term quantum devices of the quantum Internet.

Faithful Hierarchy of Genuine n-Photon Quantum Non-Gaussian Light

Light is an essential tool for connections between quantum devices and for diagnostic processes in quantum technology. Both applications deal with advanced nonclassical states beyond Gaussian coherent and squeezed states. Current development requires a loss-tolerant diagnostic of such nonclassical aspects. We propose and experimentally verify a faithful hierarchy of genuine n-photon quantum non-Gaussian light. We conclusively witnessed three-photon quantum non-Gaussian light in the experiment. Measured data demonstrate a direct applicability of the hierarchy for a large class of real states.

Beating the Rayleigh Limit Using Two-Photon Interference

Multiparameter estimation theory offers a general framework to explore imaging techniques beyond the Rayleigh limit. While optimal measurements of single parameters characterizing a composite light source are now well understood, simultaneous determination of multiple parameters poses a much greater challenge that in general requires implementation of collective measurements. Here we show, theoretically and experimentally, that Hong-Ou-Mandel interference followed by spatially resolved detection of photons provides precise information on both the separation and the centroid for a pair of point emitters, avoiding trade-offs inherent to single-photon measurements.

NIR-II nanoprobes in-vivo assembly to improve image-guided surgery for metastatic ovarian cancer

Local recurrence is a common cause of treatment failure for patients with solid tumors. Tumor-specific intraoperative fluorescence imaging may improve staging and debulking efforts in cytoreductive surgery and, thereby improve prognosis. Here, we report in vivo assembly of the second near-infrared window (NIR-II) emitting downconversion nanoparticles (DCNPs) modified with DNA and targeting peptides to improve the image-guided surgery for metastatic ovarian cancer. The NIR-II imaging quality with DCNPs is superior to that of clinically approved ICG with good photostability and deep tissue penetration (8 mm). Stable tumor retention period experienced 6 h by in vivo assembly of nanoprobes can be used for precise tumor resection. Superior tumor-to-normal tissue ratio is successfully achieved to facilitate the abdominal ovarian metastases surgical delineation. Metastases with ≤1 mm can be completely excised under NIR-II bioimaging guidance. This novel technology provides a general new basis for the future design of nanomaterials for medical applications.