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Our research is focused on generating single and entangled photons and manipulating the photon-matter interaction. Single photons are wavepackets of light energy quanta and no-cloning property. Entangled photons, on the other hand, are photon pairs with “spooky action at a distance” quoted by Einstein. With unique quantum properties, they are both essential to realizing quantum computation, quantum communication, and quantum teleportation, and to understanding quantum mechanics.

We seek to develop applications with single and entangled photons and to study the analogue between the photonic system and other physical systems by manipulating their quantum property. We use optical methods and lasers in experiments and build theoretical models to explain our observations. Our material systems include solid-state, semiconductor, or cold atom systems. This research area leads to applications as well as fundamental interests.

Research Highlights:

Ultrastable Quantum Emitter with Self-Healing Capability

Collaborating with Prof. Hao-Wu Lin, we have demonstrated optically ultrastable single-photon emitters at room temperature using the spray-synthesized CsPI3 perovskite quantum dots (PQDs). The high crystallinity and good ligand encapsulation of our PQDs enable the quantum emitters to display high brightness and high purity under continuous excitation over 24 hours. Moreover, the quantum emitters exhibit the capability of self-healing to restore their high brightness at high excitation power. The generation rate of 9106 s-1 under continuous excitation is also the highest reported thus far. Our work shows that the spray-synthesized PQDs have great potentials for the quantum technologies.

ACS Nano 15, 11358 (2021)


Purification of Single and Entangled Photons by Wavepacket Shaping

In this Review article, we review our works on applying the wavepacket shaping, an emerging quantum optics tool to manipulate the single- and entangled- photon wavefunctions, to purify single and entangled photons. Single and entangled photons lie at the heart of photonic quantum technologies, whose optimal performances are normally reached when the purity of the single or entangled photons is high. However, the multiphoton emission, dissipation, and decoherence in practical realizations always lead to the degradation of the single- and entangled- photon quality. The purification of single or entangled photons is thus valuable to restore the quantum states and enhance the performance of quantum technologies.

Adv. Quantum Technol. 4, 2000122 (2021)


Time-Resolved Detection of Photon-Surface-Plasmon Coupling

The interplay of nonclassical light and surface plasmons has attracted considerable attention due to fundamental interests and potential applications. To gain more insight into the quantum nature of the photon–surface-plasmon coupling, we demonstrated the time-resolved detection of the coupling at the single quanta level. We also realized single optical plasmons with programmable wavepacket. The time-resolved detection and coherent control of single optical plasmons can offer new opportunities to study and control the light-matter interaction at the nanoscale.

Phys. Rev. A 102, 033724 (2020)


Efficient Generation of Narrowband Entangled Photons

Biphotons with narrow bandwidth and long temporal length play a crucial role in long-distance quantum communication and linear optical quantum computing. By manipulating the two-component biphotons from a atomic ensemble, we demonstrate a highly efficient way of generating biphotons with a subnatural linewidth in the sub-MHz regime. Our work opens up the opportunity to miniaturize the biphoton source for implementing quantum technologies on chip-scale quantum devices. 

Phys. Rev. A 101, 063837 (2020)


Field Test of Quantum Key Distribution

Using an optical fiber link between National Tsing Hua University and National Chiao Tung University, we recently demonstrated Taiwan's first outdoor quantum key distribution (QKD). Secret keys are generated by sending and measuring single photons encoded with bits 0 and 1, with the key creation efficiency boosted up to 90% using the DPS protocol. Encrypted communication with these keys promises unconditional security based on the laws of physics and is also impossible for eavesdroppers to keep a transcript of communication.



Revival of Quantum Interference, Entanglement, and Nonlocality

Quantum interference and entanglement, apart from the fundamental interest, are at the heart of quantum computing and quantum communication. However, these quantum properties are easily degraded by the imperfections or limitations of the experiments. By manipulating the quantum wavepacket, we demonstrate the revival of quantum interference, entanglement, and nonlocality that would otherwise be destroyed by the distinguishability of the photons. Our study shows that these quantum features can achieve full recovery if the wavepacket manipulation is properly designed.

Phys. Rev. Lett. 123, 143601 (2019), 科技部十大科學研究之破壞性創新論文


Shaping and Purifying Single Photons from Semiconductor Nanocrystals

Colloidal quantum dots (or semiconductor nanocrystals) are promising single-photon emitters at room temperature. However, their single-photon purity is poor due to the spectrally broad bi-exciton emission. We demonstrate single-photon purification by manipulating the temporal envelope of the single photons. The purified single photons have a purity comparable to their cryogenic-temperature counterparts. Moreover, the single-photon purity does not vary with the pumping power or between different quantum dots.

Phys. Rev. Lett. 119, 143601 (2017)


Light-Matter Interaction at Single-Photon Level

Efficient light-matter interaction at the single-photon level is essential to quantum computation and quantum communication. Such interaction requires single photons of subnatural linewidth and high spectral brightness. We demonstrate a subnatural-linewidth single-photon source with the highest spectral brightness reported to date. The interaction between the single photons and atoms is also demonstrated by the controlled absorption of the single photons in an atomic vapor.

Phys. Rev. A 96, 023811 (2017)