Browsing by Author "Hsu, Li-Yi"

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Carrying an arbitrarily large amount of information using a single quantum particle
(2020-08-25)
Hsu, Li-Yi
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Lai, Ching-Yi
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Chang, You-Chia
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Wu, Chien-Ming
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Lee, Ray-Kuang
Theoretically speaking, a photon can travel arbitrarily long before it enters into a detector, resulting in a click. How much information can a photon carry? We study a bipartite asymmetric "two-way signaling" protocol as an extension of that proposed by Del Santo and Dakic. Suppose that Alice and Bob are distant from each other and each of them has an n-bit string. They are tasked to exchange the information of their local n-bit strings with each other, using only a single photon during the communication. It has been shown that the superposition of different spatial locations in a Mach-Zehnder (MZ) interferometer enables bipartite local encodings. We show that, after the travel of a photon through a cascade of n-level MZ interferometers in our protocol, the one of Alice and Bob whose detector clicks can access the other's full information of the n-bit string, while the other can gain one bit of information. That is, the wave-particle duality makes two-way signaling possible, and a single photon can carry an arbitrarily large (but finite) amount of information.
Entanglement detection via the condition of quantum correlation
(2007-09-01)
Li, Che-Ming
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Hsu, Li-Yi
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Chen, Yueh-Nan
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Chuu, Der-San
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Brandes, Tobias
We develop a necessary condition of quantum correlation. It is utilized to construct a d-level bipartite Bell-type inequality which is strongly resistant to noise and requires only analyses of O(d) measurement outcomes compared to the previous result O(d(2)). Remarkably, a connection between the arbitrary high-dimensional bipartite Bell-type inequality and entanglement witnesses is found. Through the necessary condition of quantum correlation, we propose that the witness operators to detect truly multipartite entanglement for a generalized Greenberger-Horne-Zeilinger (GHZ) state with two local measurement settings and a four-qubit singlet state with three settings. Moreover, we also propose a robust entanglement witness to detect a four-level tripartite GHZ state with only two local measurement settings.
Exploring steering effects using Bell tests
(2014-02-18)
Lo, Hsin-Pin
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Yabushita, Atsushi
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Hsu, Li-Yi
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電子物理學系
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Department of Electrophysics
We study the interconnection among steering, uncertainty, and quantum correlation. The practical steering criteria for bipartite quantum entanglement are proposed using the multiple applications of the Maassen-Uffink uncertainty relation. The results show that distant steering causes less uncertainty than that in any local-hidden-variable theories. The reduction of uncertainty in the quantum steering of entangled states leads to quantum correlation. The steering visibility for the mixed states is also discussed. The experimental results on the proposed steering criteria are reported.
QUANTUM SECRET ENCRYPTION AND DECRYPTION IN CAVITY QED
(2009-04-01)
Li, Che-Ming
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Hsu, Li-Yi
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Chuu, Der-San
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電子物理學系
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Department of Electrophysics
We present a proposal of the quantum secret encryption, transmission, and decryption implementation for quantum secret-sharing protocol using cavity QED. In the proposed scheme, the information is stored in two identical two-level atoms, and the two-qubit logic transformation is realized through the interaction between atoms and a nonresonant cavity mode. The proposed scheme requires no ancilla states to assist the intermediate atomic transitions and conditional quantum dynamics for quantum phase flip and quantum state diffusion. The encryption and decryption of quantum states are mostly governed by the Hamiltonian of an atom-cavity system. Moreover, secret transmission using quasi-swap gates for entanglement swapping has also been presented. With fewer supplements of external fields, a speed quantum protocol can be realized without universal gates.