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The construction of a large-scale quantum internet requires quantum repeaters containing multiple entangled photon sources with identical wavelengths. Semiconductor quantum dots can generate entangled photon pairs deterministically with high fidelity. However, realizing wavelength-matched quantum-dot entangled photon sources faces two difficulties: the non-uniformity of emission wavelength and exciton fine-structure splitting induced fidelity reduction. Typically, these two factors are not independently tunable, making it challenging to achieve simultaneous improvement. In this work, we demonstrate wavelength-tunable entangled photon sources based on droplet-etched GaAs quantum dots through the combined use of AC and quantum-confined Stark effects. The emission wavelength can be tuned by ~1 meV while preserving an entanglement fidelity f exceeding 0.955(1) in the entire tuning range. Based on this hybrid tuning scheme, we finally demonstrate multiple wavelength-matched entangled photon sources with f > 0.919(3), paving the way towards robust and scalable on-demand entangled photon sources for quantum internet and integrated quantum optical circuits.
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Optical vortex beams, with phase singularity characterized by a topological charge (TC), introduces a new dimension for optical communication, quantum information, and optical light manipulation. However, the evaluation of TCs after beam propagation remains a substantial challenge, impeding practical applications. Here, we introduce vortices in lateral arrays (VOILA), a novel spatial multiplexing approach that enables simultaneous transmission of a lateral array of multiple vortices. Leveraging advanced learning techniques, VOILA effectively decodes TCs, even in the presence of strong optical nonlinearities simulated experimentally. Notably, our approach achieves substantial improvements in single-shot bandwidth, surpassing single-vortex scheme by several orders of magnitude. Furthermore, our system exhibits precise fractional TC recognition in both linear and nonlinear regimes, providing possibilities for high-bandwidth communication. The capabilities of VOILA promise transformative contributions to optical information processing and structured light research, with significant potential for advancements in diverse fields.
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Quantum illumination has been proposed and demonstrated to improve the signal-to-noise ratio (SNR) in light detection and ranging (LiDAR). When relying on coincidence detection alone, such a quantum LiDAR is limited by the timing jitter of the detector and suffers from jamming noise. Inspired by the Zou-Wang-Mandel experiment, we design, construct, and validate a quantum induced coherence (QuIC) LiDAR which is inherently immune to ambient and jamming noises. In traditional LiDAR the direct detection of the reflected probe photons suffers from deteriorating SNR for increasing background noise. In QuIC LiDAR we circumvent this obstacle by only detecting the entangled reference photons, whose single-photon interference fringes are used to obtain the distance of the object, while the reflected probe photons are used to erase path information of the reference photons. In consequence, the noise accompanying the reflected probe light has no effect on the detected signal. We demonstrate such noise resilience with both LED and laser light to mimic the background and jamming noise. The proposed method paves a new way of battling noise in precise quantum electromagnetic sensing and ranging.
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Cold atoms provide a flexible platform for synthesizing and characterizing topological matter, where geometric phases play a central role. However, cold atoms are intrinsically prone to thermal noise, which can overwhelm the topological response and hamper promised applications. On the other hand, geometric phases also determine the energy spectra of particles subjected to a static force, based on the polarization relation between Wannier-Stark ladders and geometric Zak phases. By exploiting this relation, we develop a method to extract geometric phases from energy spectra of room-temperature superradiance lattices, which are momentum-space lattices of timed Dicke states. In such momentum-space lattices the thermal motion of atoms, instead of being a source of noise, provides effective forces which lead to spectroscopic signatures of the Zak phases. We measure Zak phases directly from the anti-crossings between Wannier-Stark ladders in the Doppler-broadened absorption spectra of superradiance lattices. Our approach paves the way of measuring topological invariants and developing their applications in room-temperature atoms.
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Floquet modulation has been widely used in optical lattices for coherent control of quantum gases, in particular for synthesizing artificial gauge fields and simulating topological matters. However, such modulation induces heating which can overwhelm the signal of quantum dynamics in ultracold atoms. Here we report that the thermal motion, instead of being a noise source, provides a new control knob in Floquet-modulated superradiance lattices, which are momentum-space tight-binding lattices of collectively excited states of atoms. The Doppler shifts combined with Floquet modulation provide effective forces along arbitrary directions in a lattice in frequency and momentum dimensions. Dynamic localization, dynamic delocalization, and chiral edge currents can be simultaneously observed from a single transport spectrum of superradiance lattices in thermal atoms. Our Letter paves a way for simulating Floquet topological matters in room-temperature atoms and facilitates their applications in photonic devices.
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Hydrogen bonding plays an essential role in biological processes by stabilizing proteins and lipid structures as well as controlling the speed of enzyme catalyzed reactions. Dimethyl sulfoxide-water (DMSO-H2O) solution serves as a classical model system by which the direct and indirect effects of hydrogen bonding between water hydrogens and the sulfoxide functional group can be explored. The complex transition from self-bonding to heterogeneous bonding is important, and multiple spectroscopic approaches are needed to provide a detailed assessment of those interactions. In this report, for the first time, hyper-Raman scattering was successfully employed to investigate molecular interactions in DMSO-H2O system. We measured the improper blueshift of the C-S and C-H stretching modes of DMSO caused by partial charge transfer and enhanced bond polarization. By detecting differences in the frequency shifts of C-S and C-H modes for low DMSO concentrations (<33 mol%) we find evidence of the intermolecular bonds between water and the DMSO methyl groups. We exploit the high sensitivity of hyper-Raman scattering to the low frequency librations of H2O to observe a change in librational mode population providing insight into existing questions about the coordination of H2O around DMSO molecules and the formation of the H2O shell around DMSO molecules proposed in prior simulation studies. These results demonstrate that hyper-Raman spectroscopy can be a practical spectroscopic technique to study the intermolecular bonding of model systems and test claims about model system bonding generated by theoretical calculations.
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Considering the kinetic and fluid dynamic processes in the gain medium, a theoretical model is established to describe the mechanism of thermal-lensing effect in an exciplex pumped Cs vapor laser. The three-dimensional distribution of temperature and index of refraction in the gain medium are depicted. The effective focal length and radius of thermal lens are predicted. Our simulation results show the thermal lens plays a non-negligible role in high-power XPCsLs and can be significantly aggravated in higher wall temperature, buffer pressure and pump intensity. The divergence of laser beam influenced by thermal lens is also made in detail. This model is helpful for in-depth understanding of the thermal-lensing effect in XPALs.
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A theoretical model is established to describe the kinetic processes and laser mechanism for a nanosecond-pulse exciplex pumped Cs vapor laser (XPCsL). A new simulation method is proposed to solve a set of non-stationary rate equations considering high energy levels and the results of simulation are consistent with the experimental data. The effects of cell temperature, pump energy and buffer gas on the output laser pulses are presented and analyzed in detail, which reveal the unique properties of nanosecond-pulse XPCsL.
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Considering spectrally resolved absorption and temperature distribution, a physical model is established to describe the laser kinetic and thermodynamic processes of an exciplex pumped Rb vapor laser. A comparison with Carroll's model is made. Influences of pump intensity, temperature, reflectivity of output coupler, and number density of Kr on the performance of CW Rb-Kr XPAL with uniform temperature distribution are calculated and analyzed. Besides, with the heat accumulation considered, the temperature distribution was calculated, and the maximal optical-to-optical efficiency about 5.7% can be achieved at the condition of pump intensity I0 = 5.2 × 1010 W/m2 and flow velocity u = 250 m/s.
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A physical model combining rate, power propagation, and transient heat conduction equations for diode-pumped alkali vapor lasers (DPAL) is applied to a pulsed Rb-CH4 DPAL, which agrees well with the time evolution of laser power and temperature measured by K absorption spectroscopy. The output feature and temperature rise of a multi-pulse DPAL are also calculated in the time domain, showing that if we energize the pump light when the temperature rise decays to 1/2, rather than 1/e of its maximum, we can increase the duty cycle and obtain more output energy. The repetition rate of >100Hz is high enough to achieve QCW (quasi-continuous-wave) laser pulses.
