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arXiv:2102.07044 · Journal of the Optical Society of America B

Photon conversion in thin-film lithium niobate nanowaveguides: a noise analysis

Heng Fan, Zhaohui Ma, Jia‐Yang Chen, Zhan Li, Chao Tang, Yong Meng Sua, Yu‐Ping Huang

Published Jun 10, 2021• 23 citations
arXivHTMLPDF

Abstract

Wavelength transduction of single-photon signals is indispensable to networked quantum applications, particularly those incorporating quantum memories. Lithium niobate nanophotonic devices have demonstrated favorable linear, nonlinear, and electro-optical properties to deliver this crucial function while offering superior efficiency, integrability, and scalability. Yet, their quantum noise level—a crucial metric for any single-photon-based application—has yet to be investigated. In this work, we report the first, to the best of our knowledge, study with the focus on telecom to near-visible conversion driven by a small detuned telecom pump for practical considerations in distributed quantum processing over fiber networks. Our results find the noise level to be on the order of 10 − 4 photons per time-frequency mode for high conversion, allowing faithful pulsed operations. Through carefully analyzing the origins of such noise and each’s dependence on the pump power and wavelength detuning, we have also identified a formula for noise suppression to 10 − 5 photons per mode. Our results assert a viable, low-cost, and modular approach to networked quantum processing and beyond using lithium niobate nanophotonics.

DOI
10.1364/josab.425318

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•Jan 1, 2022•0 citations
Wavelength transduction of single-photon signals is indispensable to networked quantum applications, particularly those incorporating quantum memories. Lithium niobate nanophotonic devices have demonstrated favorable linear, nonlinear, and electro-optical properties to deliver this crucial function while offering superior efficiency, integrability, and scalability. Yet, their quantum noise level—a crucial metric for any single-photon-based application—has yet to be investigated. In this work, we report the first, to the best of our knowledge, study with the focus on telecom to near-visible conversion driven by a small detuned telecom pump for practical considerations in distributed quantum processing over fiber networks. Our results find the noise level to be on the order of 10 − 4 photons per time-frequency mode for high conversion, allowing faithful pulsed operations. Through carefully analyzing the origins of such noise and each’s dependence on the pump power and wavelength detuning, we have also identified a formula for noise suppression to 10 − 5 photons per mode. Our results assert a viable, low-cost, and modular approach to networked quantum processing and beyond using lithium niobate nanophotonics.
Nanophotonic quantum memory is a vital component for scalable quantum information processing for quantum computing, networking, and sensing applications. We store single-photon-level telecom-band optical pulses for more than a microsecond using an atomic frequency comb in erbium-doped thin-film lithium niobate, well beyond what is practically feasible via propagation in even the best nanophotonic devices due to propagation losses. We verify the quantum nature of this storage by demonstrating the phase coherence and sub-single-photon noise upon retrieval. We also show the flexibility of our platform by storing up to 20 temporal modes and demonstrating an acceptance bandwidth up to 2.2 GHz. These results establish erbium-doped thin-film lithium niobate as a practical platform for on-chip quantum memory at telecom wavelengths, a key missing element for photonic quantum computing and quantum networking.
Quantum frequency conversion (QFC) plays a critical role in practical quantum information technology as it provides a bridge among different quantum devices, which usually operate at different optimal wavelength. Photons with longer wavelength feature lower propagation loss and lower solar radiation noise in free space, hence hold promise for daylight long distance quantum communication. Besides, wavelength over 2 μ m also overlap with the absorption band of many important molecules, hence is of great importance for gases and molecules detection. Yet development of technology in this region has been hindered primarily by the spectral mismatch with other quantum devices, notably quantum detection and memories, which optimally operate in the visible band. Here, we demonstrate the first QFC of 2 μ m photons to the visible region on domain-engineered thin-film lithium niobate (TFLN) platform. Benefiting from the strong nonlinearity in such integrated platform, the highest internal quantum conversion efficiency of 42% is achieved at an exceptionally low pump saturation power of only 58 mW . This work provides an efficient interconnection between photons operating at the visible and 2 μ m bands in the integrated platform, pushing forward the development of practical quantum chips for application of quantum communication, sensing and metrology in the future. • Strong mode confinement and domain-engineered thin film lithium niobate (TFLN), combined with large χ ( 2 ) , enable efficient on-chip nonlinear conversion. • First demonstration of quantum frequency conversion (QFC) of 2 μ m band photon on thin film lithium niobate.
Nanophotonic quantum memory is a vital component for scalable quantum information processing for quantum computing, networking, and sensing applications. We store single-photon-level telecom-band optical pulses for more than 1 μs using an atomic frequency comb in erbium-doped thin-film lithium niobate (TFLN), well beyond what is practically feasible via propagation in even the best nanophotonic devices due to propagation losses. We verify the quantum nature of this storage by demonstrating the phase coherence and subsingle-photon noise upon retrieval. We also show the flexibility of our platform by storing up to 20 temporal modes and demonstrating an acceptance bandwidth of up to 2.2 GHz. These results establish erbium-doped TFLN as a practical platform for on-chip quantum memory at telecom wavelengths, a key missing element for photonic quantum computing and quantum networking.
Abstract The lithium niobate on insulator (LNOI) platform has revolutionized lithium niobate materials, and a series of quantum photonic chips have exhibited unprecedented performances. Quantum frequency conversion (QFC) that enables quantum state preservation during frequency conversion is crucial in quantum technology. This work demonstrates a low-noise QFC process on the LNOI nanophotonic platform, connecting telecom and near-visible bands. An internal conversion efficiency of 73% and an on-chip noise count of 900 counts per second (cps) are achieved. Furthermore, the preservation of quantum statistical properties is verified, indicating the QFC chip’s promise for extensive applications of LNOI integrated circuits in quantum information. Based on this chip, we constructed an upconversion single-photon detector with a detection efficiency of 8.7% and a noise of 300 cps, paving the way to integrated on-chip single-photon detection. The realization of a low-noise QFC device also provide a pathway for practical chip-scale QFC-based quantum systems in heterogeneous configurations.
Efficient on-chip entangled photon pair generation at telecom wavelengths is an integral aspect of emerging quantum optical technologies, particularly for quantum communication and computing. However, moving to shorter wavelengths enables the use of more accessible silicon detector technology, and opens up applications in imaging and spectroscopy. Here, we present high brightness ((1.6 ± 0.3) × 10 9 pairs/s/mW/nm) visible–near-IR photon pair generation in a periodically poled lithium niobate nanophotonic waveguide. The degenerate spectrum of the photon pairs is centered at 811 nm with a bandwidth of 117 nm when pumped with a spectrally multimode laser diode. The measured on-chip source efficiency of (2.3 ± 0.5) × 10 11 pairs/s/mW is on par with source efficiencies at telecom wavelengths and is also orders of magnitude higher than the efficiencies of other visible sources implemented in bulk crystal or diffused waveguide-based technologies. Further improvements in the brightness and efficiencies are possible by pumping the device with a single-frequency laser, which would also shrink the pair bandwidth. These results represent the shortest wavelength of photon pairs generated in a nanophotonic waveguide reported to date by nearly an octave.
Quantum networks of superconducting qubits linked by optical channels could leverage both the quantum information processing capabilities of superconducting circuits and the long communication distances provided by optical photons. Such networks would require high efficiency, low noise, and wide bandwidth transducers between microwave and optical frequencies. Transducers based on the Pockels electro-optic (EO) effect are particularly promising in this application for their direct conversion mechanism and potential for strong performance. EO transducers could also be used for sensitive optical modulators and low-noise detection of microwave and millimeter-wave signals. This dissertation presents recent work to create cavity EO transducers in thin-film lithium niobate, an integrated photonics platform that provides low optical loss and strong EO coupling. I first describe the theory of cavity electro-optics and how it can be used to generate high-efficiency transduction between microwave and optical fields. An initial device is presented and characterized, demonstrating per-photon on-chip transduction efficiencies of up to (2.7 ± 0.3) × 10^−5. A key benefit of the device described here, which is based on photonic molecule modes, is the ability to use a static electro-optic bias to trim the transducer into resonance. However, we find the migration of free carriers in thin-film lithium niobate reduces the EO response of the device to static fields, making such trimming ineffective. This carrier migration is a key challenge for enabling the promise of low-power electro-optics provided by thin-film lithium niobate devices. I characterize the low-frequency electro-optic response, which suggests that conduction occurs on the etched surface of lithium niobate. I show how this conduction can be reduced – and low-frequency EO performance improved – by changing the electrode design and annealing the devices. Following this, I describe the design and initial characterization of an improved transducer device. Finally, I describe a scheme by which even relatively low-efficiency transducers could be used to generate remote entanglement using an optically heralding scheme. Demonstration of such a system appears possible with current devices, suggesting that small opticallymediated quantum networks of superconducting qubits may be feasible soon.