Squeezed light has evolved into a powerful tool for quantum technology, ranging from quantum-enhanced sensing and quantum-state engineering based on partial postselection techniques.The pulsed generation of squeezed light is of particular interest, as it can provide accurate time stamps and a physically defined temporal mode, which are highly preferred in complex communication networks and large-scale information processing.However, the multimode feature of pulsed squeezing limits the purity of the output state, negatively impacting its application in quantum technology.Previous demonstrations and analysis of pulsed squeezing focus on single-pass configurations and synchronously pumped free-space cavities.In this paper, we propose a different approach to generate pulsed squeezing with high temporal purity, where a parametric down-conversion process in integrated photonic cavities is pumped by a single-pass pulse.We show that the effective mode number of the output pulsed squeezing approaches unity.Such a high-purity squeezed light can be realized with broad parameters and a low pump power, providing a robust approach to generating large-scale quantum resources.
Squeezed light has evolved into a powerful tool for quantum technology, ranging from quantum-enhanced sensing and quantum-state engineering based on partial postselection techniques.The pulsed generation of squeezed light is of particular interest, as it can provide accurate time stamps and a physically defined temporal mode, which are highly preferred in complex communication networks and large-scale information processing.However, the multimode feature of pulsed squeezing limits the purity of the output state, negatively impacting its application in quantum technology.Previous demonstrations and analysis of pulsed squeezing focus on single-pass configurations and synchronously pumped free-space cavities.In this paper, we propose a different approach to generate pulsed squeezing with high temporal purity, where a parametric down-conversion process in integrated photonic cavities is pumped by a single-pass pulse.We show that the effective mode number of the output pulsed squeezing approaches unity.Such a high-purity squeezed light can be realized with broad parameters and a low pump power, providing a robust approach to generating large-scale quantum resources.
Squeezed states of light and entangled photon source are fundamental resources for quantum science and technology, enabling advances in quantum communication, computation, and precision metrology. Here, we experimentally demonstrate the generation of ultrabright squeezed vacuum and entangled photon pairs via type-I high-gain parametric down-conversion. Using femtosecond pump pulses at 1,030 nm, we produce ultrabright squeezed vacuum with pulses energies on the order of 10 μJ at a central wavelength of 2,060 nm, corresponding to a photon number exceeding 10 14 . By implementing SU(1,1) interferometric configuration, we achieve flexible control over the mode structure, allowing the transition between multimode entangled photon pairs and nearly single-mode squeezed states. This results provide a high-intensity quantum light source that facilitates the study of nonclassical ultrafast dynamics.
Squeezed light is expected to enable new quantum metrology and quantum computation applications, but the very high degree of experimental control required in practice places severe demands on the physical devices used to generate it. As ultrafast squeezed light sources are reaching an unprecedented degree of brightness and modal control, there is a strong interest in developing methods for their experimental characterization and theoretical understanding. In this thesis, we demonstrate both a new application and a new characterization technique for pulsed squeezed light. In the first part of the thesis, we present a new metrological application of pulsed squeezed light: quantum-enhanced label-free nonlinear microscopy. Stimulated emission microscopy (SEM) is a state-of-the-art pump-probe microscopy technique whose sensitivity is ultimately limited by shot noise in the probe beam. We propose to overcome this fundamental limitation by using a sub-Poissonian probe generated via optical parametric amplification. We demonstrate an intensity-squeezed sub-picosecond pulsed probe, and a simple stimulated emission microscope. Using this squeezed probe, sub-Poissonian statistics are observed in the SEM signal. After this proof-of-principle experiment, we aim to provide an improved design for a source of intensity-squeezed light. First, we develop a theoretical framework to simulate the photon statistics of a general sub-Poissonian source, considering pulsed and focused pump and seed fields in a unified spatio-temporal description. Next, we use this framework to suggest possible improvements to our previous squeezed probe. In the second part of this thesis, we provide new theoretical and experimental tools to analyze the high gain regime of pulsed spontaneous parametric down-conversion (SPDC). We study a waveguided source capable of generating twin-beams with tens of photons in a single spatio-temporal mode. We develop a framework to efficiently simulate SPDC for an arbitrary nonlinear gain, including the effect of parasitic nonlinearities such as self-phase modulation (SPM) of the pump and cross-phase modulation (XPM) between pump and twin-beams. We experimentally characterize our source using a new technique based on stimulated difference-frequency generation (DFG). In a type-II down-conversion process, we measure the frequency generation produced not only in the orthogonal polarization to the seeding beam, but also in its same polarization, which we interpret as cascaded difference-frequency generation. We argue that the additional information obtained in this measurement allows for a self-referenced estimation of the squeezing gain. Using these measurements, we accurately fit our theoretical model, revealing that, in the high gain regime, parasitic nonlinearities strongly affect the spectral structure of the twin-beams. We propose a simple strategy to reduce the impact of these nonlinearities on the modal structure of SPDC.
We present a single-pass source of broadband multimode squeezed light with potential application in quantum information and quantum metrology. The source is based on a type I parametric down-conversion (PDC) process inside a bulk nonlinear crystal in a non-collinear configuration. The generated squeezed light exhibits a spatio-temporal multimode behavior that is probed using a homodyne measurement with a local oscillator shaped both spatially and temporally. Finally we follow a covariance matrix based approach to reveal the distribution of the squeezing among several independent temporal and spatial modes. This unambiguously validates the multimode feature of our source.
Nowadays, the realization of quantum computations and communications based on continuous variables has attracted a significant attention due to a substantial expansion of the system dimensionality. The main progress in this area is attributed to the implementation of multimode systems based on squeezed states of light. One of the simplest ways to generate such states relies upon their producing in a single-pass optical parametric amplifier (OPA) using ultrafast pumping. However, for homodyne detection of such multimode states, the profile of the local oscillator (LO) must perfectly match the profile of the measured mode. Usually, this is not the case; therefore a proper treatment of multimode squeezing is required. In this work, we study both theoretically and experimentally the multimode squeezed light generated in type-0 and type-II OPA. We characterize such sources and investigate the degree of squeezing in dependence on the LO spectral profile, employing a pulse shaping technique. The theoretical analysis is performed using the Schmidt-mode theory. This work might have a significant impact on the realization of multimode quantum protocols
We present a single-pass source of broadband multimode squeezed light with potential application in quantum information and quantum metrology. The source is based on a type I parametric down-conversion (PDC) process inside a bulk nonlinear crystal in a non-collinear configuration. The generated squeezed light exhibits a spatio-temporal multimode behavior that is probed using a homodyne measurement with a local oscillator shaped both spatially and temporally. Finally we follow a covariance matrix based approach to reveal the distribution of the squeezing among several independent temporal and spatial modes. This unambiguously validates the multimode feature of our source.
Squeezed light is a fundamental nonclassical resource in quantum optics, and considerable progress has been made in its generation and manipulation. Here, we experimentally demonstrate a compact higher-order spatial modes squeezed light source, achieved by integrating second-harmonic generation and optical parametric oscillation within a single doubly resonant cavity. The HG 2 m ,2 n pump field, which is essential for the generation of HG m , n mode squeezed states, is produced via internal second-harmonic generation, substantially enhancing both the conversion efficiency and mode purity. With this configuration, we successfully generated squeezed vacuum states in the HG 0,0 , HG 1,0 , and HG 2,0 modes, achieving squeezing levels of −4.53 ± 0.26 dB, −3.68 ± 0.19 dB, and −2.58 ± 0.08 dB, respectively. This platform provides a viable pathway for scalable, multimode quantum state generation, with broad potential in quantum metrology and quantum communication.