Yin-Hai Li

Quantum twisted double-slits experiments: confirming wavefunctions’ physical reality

Abstract Are quantum states real? This most fundamental question in quantum mechanics has not yet been satisfactorily resolved, although its realistic interpretation seems to have been rejected by various delayed-choice experiments. Here, to address this long-standing issue, we present a quantum twisted double-slit experiment. By exploiting the subluminal feature of twisted photons, the real nature of a photon during its time in flight is revealed for the first time. We found that photons’ arrival times were inconsistent with the states obtained in measurements but agreed with the states during propagation. Our results demonstrate that wavefunctions describe the realistic existence and evolution of quantum entities rather than a pure mathematical abstraction providing a probability list of measurement outcomes. This finding clarifies the long-held misunderstanding of the role of wavefunctions and their collapse in the evolution of quantum entities.

On-Chip Multiplexed Multiple Entanglement Sources in a Single Silicon Nanowire

Silicon-on-chip (SOI) photonic circuit is the most promising platform for scalable quantum information technology for its low loss, small footprint, CMOS-compatible and telecom communications techniques compatible. Multiple multiplexed entanglement sources include: energy-time, time-bin and polarization entangled sources based on 1-cm length single silicon nanowire, all these sources are compatible with (100GHz) dense-wave-division-multiplexing (DWDM) system. Different methods such as two photon interference pattern, Bell-Inequality and quantum state tomography are used to characterize the quality of these entangled sources. Multiple entanglements are generated over more than 5 channel pairs with high raw (net) visibilities around 97% (100%). The emission spectral brightness of these entangled sources reaches 4.2*105 /(s.nm.mW). The quality of the photon pair generated in continuous and pulse pump regimes are compared. High qualities of these multiplexed entanglement sources make them very promising to be used in future minimized quantum communication and computation systems.

Superresolving Phase Measurement with Short-Wavelength NOON States by Quantum Frequency Up-Conversion

Precise measurements are the key to advances in all fields of science. Quantum entanglement shows higher sensitivity than achievable by classical methods. Most physical quantities including position, displacement, distance, angle, and optical path length can be obtained by optical phase measurements. Reducing the photon wavelength of the interferometry can further enhance the optical path length sensitivity and imaging resolution. By quantum frequency up conversion, we realized a short wavelength two photon number entangled state. Nearly perfect Hong Ou Mandel interference is achieved after both 1547-nm photons are up converted to 525 nm. Optical phase measurement of two photon entanglement state yields a visibility greater than the threshold to surpass the standard quantum limit. These results offer new ways for high precision quantum metrology using short wavelength quantum entanglement number state.

Multiplexed entangled photon-pair sources for all-fiber quantum networks

The ultimate goal of quantum information science is to build a global quantum network, which enables quantum resources to be distributed and shared between remote parties. Such a quantum network can be realized using only fiber elements, thus deriving the advantages of low transmission loss, low cost, scalability, and integrability through mature fiber communication techniques such as dense wavelength division multiplexing. Hence high-quality entangled-photon sources based on fibers are in high demand. Here we report multiplexed polarization- and time-bin-entangled photon-pair sources based on the dispersion-shifted fiber operating at room temperature. The associated high quality of entanglement is characterized using interference, Bell’s inequality, and quantum state tomography. The simultaneous presence of both types of entanglement in multi-channel pairs of a 100-GHz dense wavelength division multiplexing device indicates a great capacity in distributing entangled photons over multiple users. Our design provides a versatile platform and takes a big step toward constructing an all-fiber quantum network.

Efficient 525 nm laser generation in single or double resonant cavity

Abstract This paper reports the results of a study into highly efficient sum frequency generation from 792 and 1556 nm wavelength light to 525 nm wavelength light using either a single or double resonant ring cavity based on a periodically poled potassium titanyl phosphate crystal (PPKTP). By optimizing the cavity’s parameters, the maximum power achieved for the resultant 525 nm laser was 263 and 373 mW for the single and double resonant cavity, respectively. The corresponding quantum conversion efficiencies were 8 and 77% for converting 1556 nm photons to 525 nm photons with the single and double resonant cavity, respectively. The measured intra-cavity single pass conversion efficiency for both configurations was about 5%. The performances of the sum frequency generation in these two configurations was studied and compared in detail. This work will provide guidelines for optimizing the generation of sum frequency generated laser light for a variety of configurations. The high conversion efficiency achieved in this work will help pave the way for frequency up-conversion of non-classical quantum states, such as the squeezed vacuum and single photon states. The proposed green laser source will be used in our future experiments, which includes a plan to generate two-color entangled photon pairs and achieve the frequency down-conversion of single photons carrying orbital angular momentum.

Coherent frequency bridge between visible and telecommunications band for vortex light

In quantum communications, vortex photons can encode higher-dimensional quantum states and build highdimensional communication networks (HDCNs). The interfaces that connect different wavelengths are significant in HDCNs. We construct a coherent orbital angular momentum (OAM) frequency bridge via difference frequency conversion in a nonlinear bulk crystal. Using a single resonant cavity, maximum quantum conversion efficiencies from visible to infrared are 36%, 15%, and 7.8% for topological charges of 0,1, and 2, respectively. The average fidelity obtained using quantum state tomography for the down-converted infrared OAM-state of topological charge 1 is 96.51%. We also prove that the OAM is conserved in this process by measuring visible and infrared interference patterns. This coherent OAM frequency-down conversion bridge represents a basis for an interface between two high-dimensional quantum systems operating with different spectra.