Photonic Frequency Conversion Research Articles

Metropolitan-scale heralded entanglement of solid-state qubits.

A key challenge toward future quantum internet technology is connecting quantum processors at metropolitan scale. Here, we report on heralded entanglement between two independently operated quantum network nodes separated by 10 kilometers. The two nodes hosting diamond spin qubits are linked with a midpoint station via 25 kilometers of deployed optical fiber. We minimize the effects of fiber photon loss by quantum frequency conversion of the qubit-native photons to the telecom L-band and by embedding the link in an extensible phase-stabilized architecture enabling the use of the loss-resilient single-click entangling protocol. By capitalizing on the full heralding capabilities of the network link in combination with real-time feedback logic on the long-lived qubits, we demonstrate the delivery of a predefined entangled state on the nodes irrespective of the heralding detection pattern. Addressing key scaling challenges and being compatible with different qubit systems, our architecture establishes a generic platform for exploring metropolitan-scale quantum networks.

Controllable nonreciprocal single-photon frequency converter via a four-level system

We propose an efficient, nonreciprocal single-photon device that achieves single-photon routing and frequency conversion through chiral coupling of two one-dimensional waveguides with a four-level atom. Photons incoming from one port can be definitely directed to another port. However, the photon frequency conversion has been achieved only when the single photons are transferred from one waveguide to the other, and its probability can reach unity. Applied the on-demand classical field to drive an atom, the transmission quantum tunneling path can be turned off and on by exploiting the Autler–Townes splitting mechanism. Our results illustrate the potential of our device for applications in a quantum network.

Two‐Stage, Low Noise Quantum Frequency Conversion of Single Photons from Silicon‐Vacancy Centers in Diamond to the Telecom C‐Band

AbstractThe silicon‐vacancy center in diamond holds great promise as a qubit for quantum communication networks. However, since the optical transitions are located within the visible red spectral region, quantum frequency conversion to low‐loss telecommunication wavelengths becomes a necessity for its use in long‐range, fiber‐linked networks. This work presents a highly efficient, low‐noise quantum frequency conversion device for photons emitted by a silicon‐vacancy (SiV) center in diamond to the telecom C‐band. By using a two‐stage difference‐frequency mixing scheme, spontaneous parametric down‐conversion (SPDC) noise is circumvented and Raman noise is minimized, resulting in a very low noise rate of 10.4 ± 0.7 photons per second as well as an overall device efficiency of 35.6%. By converting single photons from SiV centers, it demonstrates the preservation of photon statistics upon conversion.

Coherent stepped-frequency waveform generation based on recirculating microwave photonic frequency conversion.

We propose a novel method for generating coherent and wideband stepped-frequency waveforms using recirculating microwave photonic frequency conversion (MWP-FC). By injecting a narrowband signal into an MWP-FC loop utilizing a dual-parallel Mach-Zehnder modulator (DPMZM), the signal frequency is continuously converted to produce a stepped-frequency waveform with a wide bandwidth. Within the MWP-FC loop, photo-electric conversion is achieved based on self-mixing detection, where the optical phase noise can be suppressed, guaranteeing stability and coherence of the generated signal. In a proof-of-concept experiment, a stepped-frequency signal with a frequency interval of 2 GHz and a bandwidth of about 16 GHz and a stepped-frequency chirp signal with a frequency interval of 3 GHz and a bandwidth of about 15 GHz are generated. In addition, coherence of the generated signals is verified by coherent integration and de-chirping.

Low-Noise Quantum Frequency Conversion of Photons from a Trapped Barium Ion to the Telecom O-band

Low-Noise Quantum Frequency Conversion of Photons from a Trapped Barium Ion to the Telecom O-band

Frequency conversion in a hybrid cavity-optomechanical system

We propose a scheme to realize frequency conversion of photons, using a hybrid system with a qubit coupled to both a resonator cavity and an optomechanical cavity. In this system, a high-energy photon can be converted into a low-energy photon plus a phonon and vice versa; the qubit works as an intermediate medium with its states unchanged. Moreover, the process can be exquisitely tuned by changing the frequency of the qubit or the resonator mode, providing additional control for the conversion. We further analyze the system dynamics and demonstrate two Rabi oscillation behaviors with dissipations. With the state-of-the-art techniques in cavity quantum electrodynamics and optomechanical systems, our proposal would be implemented and an efficient and controllable quantum light source can be achieved.

Coherent resonant coupling between atoms and a mechanical oscillator mediated by cavity-vacuum fluctuations

We show that an atom can be coupled to a mechanical oscillator via quantum vacuum fluctuations of a cavity field enabling energy transfer processes between them. In a hybrid quantum system consisting of a cavity resonator with a movable mirror and an atom, these processes are dominated by two pair-creation mechanisms: the counterrotating (atom-cavity system) and dynamical Casimir interaction terms (optomechanical system). Because of these two pair-creation mechanisms, the resonant atom-mirror coupling is the result of high-order virtual processes with different transition paths well described in our theoretical framework. We perform a unitary transformation to the atom-mirror system Hamiltonian, exhibiting two kinds of multiple-order transitions of the pair creation. By tuning the frequency of the atom, we show that photon frequency conversion can be realized within a cavity of multiple modes. Furthermore, when involving two atoms coupled to the same mechanical mode, a single vibrating excitation of the mechanical oscillator can be simultaneously absorbed by the two atoms. Considering recent advances in strong and ultrastrong coupling for cavity optomechanics and other systems, we believe our proposals can be implemented using available technology.

Strong Kinetic-Inductance Kerr Nonlinearity with Titanium Nitride Nanowires

The kinetic inductance of charge carriers in disordered superconductors provides a broadband low-loss source of nonlinear electromagnetic response. This work investigates TiN nanowires as an alternative to Josephson junctions for applications involving elevated temperatures, higher frequencies, and strong magnetic fields. An extreme nanowire geometry for TiN microwave resonators leads to current-density concentration and enhanced self-Kerr coefficient, yielding a nonlinearity-to-loss ratio as high as 21% and quality factor exceeding 10,000. Such devices may find application in quantum frequency conversion of microwave photons, and with improvement might attain strong quantum nonlinearity.

Improving the Signal-to-Noise Ratio of Photonic Frequency Conversion from 852 nm to 1560 nm Based on a Long-Wavelength Laser-Pumped PPLN Waveguide Module

The storage wavelength of quantum nodes based on atomic systems does not match the wavelength of optical fiber communication, which requires the establishment of an efficient conversion system between flying bits and storage bits. In this paper, based on the nonlinear wavelength conversion technology of the periodically poled lithium niobate waveguide, a low-noise conversion of 852-nm photons to 1560-nm photons was achieved by a 1878-nm pump laser. The generation mechanism and transmission mechanism of noise due to nonlinear process are analyzed theoretically. The noise photons introduced by the spontaneous parameter downconversion and spontaneous Raman scattering process of a strong pump laser are experimentally studied. The noise suppression near 1560 nm is realized by the fiber Bragg grating (FBG) filter. In the experiment, when the FBG bandwidth is reduced from 0.257 nm to 0.130 nm, the signal-to-noise ratio (SNR) increases from 52 to 90. Our results show that the SNR can be greatly improved by using a narrower band filter. Therefore, the quantum node is connected to the fiber channel, and the signal can be transmitted over long distances with low loss and high fidelity.

Ultratunable Quantum Frequency Conversion in Photonic Crystal Fiber.

Quantum frequency conversion of single photons between wavelength bands is a key enabler to realizing widespread quantum networks. We demonstrate the quantum frequency conversion of a heralded 1551nm photon to any wavelength within an ultrabroad (1226-1408nm) range in a group-velocity-symmetric photonic crystal fiber, covering over 150 independent frequency bins. The target wavelength is controlled by tuning only a single pump laser wavelength. We find internal, and total, conversion efficiencies of 12(1)% and 1.4(2)%, respectively. For the case of converting 1551 to 1300nm we measure a heralded g^{(2)}(0)=0.25(6) for converted light from an input with g^{(2)}(0)=0.034(8). We expect that this photonic crystal fiber can be used for myriad quantum networking tasks.

Quantum frequency conversion with coherent transfer of time-bin encoding

Time-bin encoding of photons offers a robust kind of long-distance quantum communication over lossy channels. The diversity of material nodes in quantum networks operating at natural frequencies requires coherent frequency and wave-form conversion of information-carrying photons to provide an efficient quantum interface with optical fibers and various quantum memories, which has been extensively studied. However, the quantum frequency conversion with transfer of time-bin encoding between single photons of different wavelengths has not yet been explored. In this paper, we present a method for efficiently exchanging time-bin encoding in the conversion process between two photons propagating in cold tripod atoms driven by a strong laser field. The latter is designed to slow down photons and suppress their absorption due to electromagnetically induced transparency. Photons interact parametrically through modified atomic coherence, which is utilized also to achieve equal group velocities of photons. We demonstrate the ability of our model to generate entanglement between distant atoms that equally share the original quantum information stored in the ground-state polarization qubits of both atoms. The proposed method for frequency conversion based on modified atomic coherence is promising because it can simplify the implementation of reliable and high-speed quantum communication protocols based on single-photon entanglement.

Tunable and state-preserving frequency conversion of single photons in hydrogen.

In modern quantum technologies, preservation of the photon statistics of quantum optical states upon frequency conversion holds the key to the viable implementation of quantum networks, which often require interfacing of several subsystems operating in widely different spectral regions. Most current approaches offer only very small frequency shifts and limited tunability, while suffering from high insertion loss and Raman noise originating in the materials used. We introduce a route to quantum-correlation-preserving frequency conversion using hydrogen-filled antiresonant-reflecting photonic crystal fibers. Transient optical phonons generated by stimulated Raman scattering enable selective frequency up-conversion by 125 terahertz of the idler photon of an entangled pair, with efficiencies up to 70%. This threshold-less molecular modulation process preserves quantum correlations, making it ideal for applications in quantum information.

A Photonics-Based Superheterodyne RF Reception Approach

A novel photonics-based RF reception approach is proposed as a competitive solution to meet the current challenges of photonics-based approaches and to realize high performances at the same time. The proposed approach adopts the superheterodyne configuration by a combination manner of electronic techniques and photonic techniques, including the ultra-wideband generation of optical LO, the two-stage photonic superheterodyne frequency conversion and the real-time IF compensation. An engineering prototype has been developed and its performance has been evaluated in the laboratory environment. The experiment results preliminarily verify the feasibility of the proposed approach and its engineering potential. The typical performances are as follows: 0.1 GHz ~ 45 GHz operation spectrum range (> 40 GHz), 900 MHz instantaneous bandwidth, 101 dB·Hz2/3 SFDR and 130 dB·Hz LDR, image rejections of ~ 80 dB for 1st frequency conversion and > 90 dB for 2nd frequency conversion.

Photonic Frequency Conversion of OFDM Microwave Signals in a Wavelength‐Scale Optomechanical Cavity

AbstractOptomechanical (OM) cavities enable coupling of near‐infrared light and GHz‐frequency acoustic waves in wavelength‐scale volumes. When driven in the phonon lasing regime, an OM cavity can perform simultaneously as a nonlinear mixer and a local oscillator—at integer multiples of the mechanical resonance frequency—in the optical domain. In this work, this property is used to demonstrate all‐optical frequency down‐ and up‐conversion of MHz‐bandwidth orthogonal frequency division multiplexed signals compliant with the IEEE 802.16e WiMAX wireless standard at microwave frequencies. To this end, a silicon OM crystal cavity (OMCC), supporting a breathing‐like mechanical resonance at GHz and having a foot‐print 10 m, which yields frequency conversion efficiencies better than −17 dB in both down‐ and up‐conversion processes at mW‐scale driving power, is employed. This work paves the way toward the application of OMCCs in low‐power all‐photonic processing of digitally modulated microwave signals in miniaturized silicon photonics chips.

Photonic broadband signal frequency conversion and bandwidth multiplication based on a Fourier domain mode-locked optoelectronic oscillator

A photonic broadband signal frequency conversion and bandwidth multiplication system is demonstrated based on a Fourier domain mode-locked optoelectronic oscillator (FDML-OEO). In this method, frequency conversion is achieved by using the selected optical sideband as the optical source of the FDML-OEO. An experiment is conducted, and a linear frequency modulation (LFM) signal with different central frequencies are converted. The central frequency of the converted signal can be tuned simply by adjusting the wavelength of the optical carrier. Due to the feature of low phase noise of the OEO, the degradation of the converted signal is almost neglected. Broadband signals with different time widths are also converted in terms of fibre length regulation. Furthermore, bandwidth multiplication of the LFM signal is achieved by selecting a second-order optical sideband as the optical source of the FDML-OEO.

C-band single photons from a trapped ion via two-stage frequency conversion

Fiber-based quantum networks require photons at telecommunications wavelengths to interconnect qubits separated by long distances. Trapped ions are leading candidates for quantum networking with high-fidelity two-qubit gates, long coherence times, and the ability to readily emit photons entangled with the ion's internal qubit states. However, trapped ions typically emit photons at wavelengths incompatible with telecommunications fiber. Here, we demonstrate frequency conversion of visible photons, emitted from the S–P dipole transition of a trapped Ba+ ion into the telecommunications C-band. These results are an important step toward enabling a long-distance trapped ion quantum internet.

Group-velocity symmetry in photonic crystal fibre for ultra-tunable quantum frequency conversion

Low-noise frequency conversion of single photons is a critical tool in establishing fibre-based quantum networks. We show that a single photonic crystal fibre can achieve frequency conversion by Bragg-scattering four-wave mixing of source photons from an ultra-broad wavelength range by engineering a symmetric group velocity profile. Furthermore, we discuss how pump tuning can mitigate realistic discrepancies in device fabrication. This enables a single highly adaptable frequency conversion interface to link disparate nodes in a quantum network via the telecoms band.

Photon pumping in a weakly-driven quantum cavity–spin system

We investigate the photon pumping effect in a topological model consisting of a periodically driven spin-1/2 coupled to a quantum cavity mode out of the adiabatic limit. In the strong-drive adiabatic limit, a quantized frequency conversion of photons is expected as the temporal analog of the Hall current. We numerically establish a novel photon pumping phenomenon in the experimentally accessible nonadiabatic driving regime for a broad region of the parameter space. The photon frequency conversion efficiency exhibits strong fluctuations and high efficiency that can reach up 80% of the quantized value for commensurate frequency combinations. We link the pumping properties to the delocalization of the corresponding Floquet states which display multifractal behavior as the result of hybridization between localized and delocalized sectors. Finally we demonstrate that the quantum coherence properties of the initial state are preserved during the frequency conversion process in both the strong and ultra-weak-drive limit.

Improving entanglement generation rates in trapped-ion quantum networks using nondestructive photon measurement and storage

Long range quantum information processing will require the integration of different technologies to form hybrid architectures combining the strengths of multiple quantum systems. In this work, we propose a hybrid networking architecture designed to improve entanglement rates in quantum networks based on trapped ions. Trapped ions are excellent candidates as network nodes but photon losses make long-distance networking difficult. To overcome some losses and extend the range of trapped-ion-based networks, we propose including neutral-atom-based non-destructive single-photon detection and single photon storage in between networking nodes, forming a hybrid network. This work builds on recently demonstrated optical frequency conversion of single photons emitted by trapped ions. We derive the average two-node entanglement rate for this proposed network architecture as a function of distance. Using reasonable experimental parameters, we show this proposed quantum network can generate remote entanglement rates up to a factor of 100 larger than that of an equivalent homogeneous network at both near-IR and C-band wavelengths for distances up to 50 km.

Visible‐to‐Ultraviolet Light Conversion: Materials and Applications

Photon frequency conversion using optical materials is a common strategy for light generation and utilization. Materials capable of visible‐to‐ultraviolet (UV) light conversion have attracted particular attention due to their potential applications in nonlinear optics, biophotonics, as well as environmental sciences. There are four main mechanisms of visible‐to‐UV light conversion processes, including second‐harmonic generation, two‐photon absorption, lanthanide‐based upconversion, and triplet–triplet annihilation. Herein, recent developments in visible‐to‐UV light conversion materials are collectively reviewed and the emerging applications are presented. The prospects and challenges for further development in this field are also highlighted.