Quantum technology employs the ‘spooky’ phenomena of quantum physics such as superposition, randomness and entanglement to process information in a novel way. Quantum photonics provides a promising path for both delivering quantum-enhanced technologies and exploring fundamental physics. In this talk, I will introduce our recent work on quantum delayed-choice experiment based on multiphoton entangled states, which shows that a photon can not only be a particle or wave, but the superposition of them, even under Einstein’s locality condition. In the second part of my talk, I will present our recent endeavors in developing functional nodes for quantum information processing based on integrated optics architecture and their potential applications in a metropolitan fiber network.

The measurement of minuscule forces and displacements with ever greater precision is inhibited by the Heisenberg uncertainty principle, which imposes a the standard quantum limit (SQL). The way to surpass SQL is by introducing correlations between the position/momentum uncertainty of the object and the photon number/phase uncertainty of the light that it reflects. Authors confirm experimentally the theoretical prediction that this type of quantum correlation is naturally produced in the Laser Interferometer Gravitational-wave Observatory (LIGO). They characterize and compare noise spectra taken without squeezing and with squeezed vacuum states injected at varying quadrature angles. After subtracting classical noise, measurements show that the quantum mechanical uncertainties in the phases of the 200-kilowatt laser beams and in the positions of the 40-kilogram mirrors of the Advanced LIGO detectors yield a joint quantum uncertainty that is a factor of 1.4 (3 decibels) below the standard quantum limit. Authors anticipate that the use of quantum correlations will improve not only the observation of gravitational waves, but also more broadly future quantum noise-limited measurements.

As an important candidate for quantum simulation and quantum computation, a microscopic array of single atoms confined in optical dipole traps is advantageous in controlled interaction, long coherence time and scalability of providing thousands of qubits in a small footprint of less than 1mm$^2$. Recently, several breakthroughs have greatly advanced the application of neutral atom system in quantum simulation and quantum computation, such as atom-by-atom assembling of defect-free arbitrary atomic arrays, single qubit addressing and manipulating in 2D and 3D array, extending coherence time of atomic qubits, C-NOT gate based on Rydberg interactions, high fidelity readout and so on. In this talk, the experimental progress towards quantum computation based on neutral atoms is reviewed, along with several contributions done by our group. First, a magic-intensity trapping technique is developed to mitigate the detrimental decoherence effects which is induced by light shift, and substantially enhanced the coherence time to 225 ms which have improved our previous coherence time by a factor of 100. This technique is later used to improve the single qubit opeartion fidelity to over 0.9999. Second, the difference in the resonant frequencies of the two atoms of different isotopes is exploited to avoid the crosstalk of individually addressing and manipulating nearby atoms. Based on this heteronuclear single atom system, the heteronuclear controlled-NOT (CNOT) quantum gate and entanglement of a Rb-85 atom and a Rb-87 atom is demonstrated via Rydberg blockade for the first time. These results will trigger the quest for new protocols and schemes to use the double species for quantum computation with neutral atoms. In the end, the challenges for further development of neutral atom system in quantum simulation and quantum computation are outlooked.

Optical coherence tomography (OCT) is a highly successful 3D imaging technique that was put forward in 1991 Standard OCT schemes make use of a Michelson interferometer, and achieve high axial resolution using light with a large bandwidth. In the last few years, there has been a growing interest in a new type of OCT schemes that uses so-called nonlinear interferometers based on optical parametric amplifiers. Some of these OCT schemes are based on the idea of induced coherence, a particular class of nonlinear interferometer originally introduced the very same year as OCT. Other schemes are based on an SU(1,1) interferometer. All of these experimental demonstrations have been done in the low parametric gain regime, where the low energy available requires long integration times to achieve high quality imaging. In this regime one needs to use single photon counting modules for signal detection. We show that one can do optical coherence tomography based on an SU(1,1) nonlinear interferometer with high-gain parametric down-conversion. For imaging and sensing applications, this scheme promises to outperform previous experiments working at low arametric gain, since higher photon fluxes provide better sensitivity and lower integration times for obtaining high-quality images. Moreover, there is no need to use single-photon detectors and standard spectrometers can be used instead.