arXiv subjects

Fang-Yu Hong

Publications and source records attributed to Fang-Yu Hong.

18 recordsLinked to original sources

arXiv2026

A Universal Topological Platform for Nonreciprocal Spin-Photon Interface in Solid-State Quantum Networks

A fundamental obstacle to scalable solid-state quantum networks is the lack of a universal interface providing strong light-matter coupling, deterministic nonreciprocal photon routing, and efficient extraction. Here we propose a plasmonic platform overcoming these challenges using a Tomonaga-Luttinger liquid (TLL) in a single-walled carbon nanotube (SWCNT) microtoroid. The TLL's collective bosonic excitations are kinematically protected against backscattering by a large valley-momentum mismatch, guaranteeing robust chiral spin-momentum locking unattainable in dielectric cavities. This 1D protection enables deterministic routing of circularly polarized photons from a quantum emitter (e.g., a nitrogen-vacancy center) into distinct propagation channels. By aligning the emitter's symmetry axis, parasitic {\pi} transitions are geometrically forbidden. Furthermore, residual atomic-scale backscattering is suppressed to ~100 Hz via electrostatic gating and annealing. To overcome the severe mode mismatch between the CNT plasmon and optical fiber, we introduce a graded plasmonic-photonic mode converter, providing a path to near-unity extraction efficiency. Using a tripod-STIRAP scheme, we demonstrate high-fidelity, magnetically tunable spin-photon entanglement. Our analysis confirms operation deep in the strong-coupling regime, with cooperativities C > 100 and chiral contrast exceeding 20 dB. This wavelength-agnostic architecture is compatible with any solid-state emitter, establishing a scalable blueprint for robust, nonreciprocal quantum nodes in a global quantum internet.

quant-ph↗

arXiv2024

Electrically-Driven and Exponentially-Enhanced Spin-Photon Interfaces for Quantum Networks

We present an electrically-driven scheme for spin-photon quantum interfaces used in quantum networks. Through modulating the motion of a nano cantilever with voltages, optomechanical coupling and spin-mechanical coupling can be exponentially enhanced simultaneously. Numerical simulations show that by applying well-designed voltages high-fidelity quantum interface operations such as generation and absorption of a single-photon with a known wave packet are within the reach of current techniques.

quant-ph↗

arXiv2016

Electrically tunable quantum interfaces between photons and spin qubits in carbon nanotube quantum dots

We present a new scheme for quantum interfaces to accomplish the interconversion of photonic qubits and spin qubits based on optomechanical resonators and the spin-orbit-induced interactions in suspended carbon nanotube quantum dots. This interface implements quantum spin transducers and further enables electrical manipulation of local electron spin qubits, which lays the foundation for all-electrical control of state transfer protocols between two distant quantum nodes in a quantum network. We numerically evaluate the state transfer processes and proceed to estimate the effect of each coupling strength on the operation fidelities.

quant-ph↗

arXiv2015

Electrical Control of Strong Spin-Phonon Coupling in a Carbon Nanotube

We describe an approach to electrically control the strong interaction between a single electron spin and the vibrational motion of a suspended carbon nanotube resonator. The strength of the deflection-induced spin-phonon coupling is dependent on the wavefunction of the electron confined in a lateral carbon nanotube quantum dot. An electrical field along the nanotube shifts the effective center of the quantum dot, leading to the corresponding modification of the spin-phonon strength. Numerical simulations with experimentally reachable parameters show that high fidelity quantum state transfer between mechanical and spin qubits driven by electrical pulses is feasible. Our results form the basis for the fully electrical control of the coherent interconvertion between light and spin qubits and for manufacturing electrically driven quantum information processing systems.

quant-ph↗

arXiv2013

Quantum Information Transfer between Topological and Superconducting Qubits

We describe a scheme that enables a strong Jaynes-Cummings coupling between a topological qubit and a superconducting flux qubit. The coupling strength is dependent on the phase difference between two superconductors on a topological insulator and may be expediently controlled by a phase controller. With this coherent coupling and single-qubit rotations arbitrary unitary operations on the two-qubit hybrid system of topological and flux qubits can be performed. Numerical simulations show that quantum state transfer and entanglement distributing between the topological and superconducting flux qubits may be performed with high fidelity.

quant-ph↗

arXiv2013

Strong Coupling between a Topological Qubit and a Nanomechanical Resonator

We describe a scheme that enables a strong coherent coupling between a topological qubit and the quantized motion of a magnetized nanomechanical resonator. This coupling is achieved by attaching an array of magnetic tips to a namomechanical resonator under a quantum phase controller which coherently controls the energy gap of a topological qubit. Combined with single-qubit rotations the strong coupling enables arbitrary unitary transformations on the hybrid system of topological and mechanical qubits and may pave the way for the quantum information transfer between topological and optical qubits. Numerical simulations show that quantum state transfer and entanglement distributing between the topological and mechanical qubits may be accomplished with high fidelity.

quant-ph↗

arXiv2012

The essence of microphysical entities

In spite of its outstanding success, quantum mechanics remains mysterious, many problems such as wave/particle dualism and quantum nonlocality remain open. Because a particle, e.g. a photon, is a quantum of a corresponding quantum field, an arbitrary particle state directly corresponds to a quantum field, which shows the quantum field is nonlocal. A microphysical entity (ME) can be taken as the corresponding quantum field which is in the state of a quantum, where the quantum field is responsible for the ME's wave-like nature and the quantum for the ME's particle-like nature. A quantum state directly corresponds to a quantum field. Base on this simple model, many big problems in quantum physics, such as the wave/particle dualism, the collapse of the quantum state on measurement, the nonlocality in quantum entanglement, quantum teleportation, quantum swapping, and the paradox in the delayed-choice entanglement swapping, can be solved in very simple and natural manners.

quant-ph↗

arXiv2012

A Robust Quantum Random Access Memory

A "bucket brigade" architecture for a quantum random memory of $N=2^n$ memory cells needs $n(n+5)/2$ times of quantum manipulation on control circuit nodes per memory call. Here we propose a scheme, in which only average $n/2$ times manipulation is required to accomplish a memory call. This scheme may significantly decrease the time spent on a memory call and the average overall error rate per memory call. A physical implementation scheme for storing an arbitrary state in a selected memory cell followed by reading it out is discussed.

quant-ph↗

arXiv2010

Efficient excitation of a symmetric collective atomic state with a single-photon through dipole blockade

In the famous quantum communication scheme developed by Duan {\it et al.}[L.M. Duan, M.D. Lukin, J.I. Cirac, and P. Zoller, Nature (London) {\bf 414} 413 (2001)], the probability of successful generating a symmetric collective atomic state with a single-photon emitted have to be far smaller than 1 to obtain an acceptable entangled state. Because of strong dipole-dipole interaction between two Rydberg atoms, more than one simultaneous excitations in an atomic ensembles are greatly suppressed, which makes it possible to excite a mesoscopic cold atomic ensemble into a singly-excited symmetric collective state accompanied by a signal photon with near unity success probability, at the same higher-order excitations can be significantly inhibited.

quant-ph↗

arXiv2010

Long-distance quantum communication with "polarization" maximally entangled states

We propose a scheme for long-distance quantum communication where the elementary entanglement is generated through two-photon interference and quantum swapping is performed through one-photon interference. Local "polarization" maximally entangled states of atomic ensembles are generated by absorbing a single photon from on-demand single-photon sources. This scheme is robust against phase fluctuations in the quantum channels, moreover speeds up long-distance high-fidelity entanglement generation rate.

quant-ph↗

arXiv2010

The origin of quantum nonlocality

Quantum entanglement is the quintessential characteristic of quantum mechanics and the basis for quantum information processing. When one of two maximally entangled particles is measured, without measurement the state of another one is determined simultaneously no matter how far the two particles is from each other. How can these phenomena take place since no object can move faster than light speed in a vacuum? The key problem is due to the ignorance of the interaction between a particle and a quantum vacuum. Just like the case where a gun suffers recoil from its firing of a bullet, when a particle is created from the quantum vacuum, the vacuum will be somewhat "broken" correspondingly, which can be described by a shadow state in the vacuum. Through their shadows in the vacuum two quantum entangled particles can have a distance-independent instantaneous interaction with each other. Quantum teleportation, quantum swap, and wave function collapse are explained in a similar way. Quantum object can be interpreted as a composite made up of a particle and the shadowed quantum vacuum which is responsible for the wave characteristic of the particle wave duality. The quantum vacuum is not only the origin of all possible kinds of particles, but also the origin and the core of Eastern mystics.

quant-ph↗

arXiv2009

Proposal for a loophole-free Bell test with electron spins of donors

So far, all experimental tests of Bell inequalities which must be satisfied by all local realistic hidden-variable theories and are violated by quantum mechanical predictions have left at least one loophole open. We propose a feasible setup allowing for a loophole-free test of the Bell inequalities. Two electron spin qubits of phosphorus donors in semiconductors in different cavities 300 m apart are entangled through a bright coherent light and postselections using homodyne measurements. The electron spins are then read out randomly and independently by Alice and Bob, respectively, with unity efficiency in less than 0.7$μ$s by using optically induced spin to charge transduction detected by radio-frequency single electron transistor. A violation of Bell inequality larger than 37% and 18% is achievable provided that the detection accuracy is 0.99 and 0.95, respectively.

quant-ph↗

arXiv2008

Robust quantum repeater with atomic ensembles and single-photon sources

We present a quantum repeater protocol using atomic ensembles, linear optics and single-photon sources. Two local 'polarization' entangled states of atomic ensembles $u$ and $d$ are generated by absorbing a single photon emitted by an on-demand single-photon sources, based on which high-fidelity local entanglement between four ensembles can be established efficiently through Bell-state measurement. Entanglement in basic links and entanglement connection between links are carried out by the use of two-photon interference. In addition to being robust against phase fluctuations in the quantum channels, this scheme may speed up quantum communication with higher fidelity by about 2 orders of magnitude for 1280 km compared with the partial read (PR) protocol (Sangouard {\it et al.}, Phys. Rev. A {\bf77}, 062301 (2008)) which may generate entanglement most quickly among the previous schemes with the same ingredients.

quant-ph↗

arXiv2008

Quantum Communications with Compressed Decoherence Using Bright Squeezed Light

We propose a scheme for long-distance distribution of quantum entanglement in which the entanglement between qubits at intermediate stations of the channel is established by using bright light pulses in squeezed states coupled to the qubits in cavities with a weak dispersive interaction. The fidelity of the entanglement between qubits at the neighbor stations (10 km apart from each other) obtained by postselection through the balanced homodyne detection of 7 dB squeezed pulses can reach F=0.99 without using entanglement purification, at same time, the probability of successful generation of entanglement is 0.34.

quant-ph↗

arXiv2008

Quantum Interfaces Using Nanoscale Surface Plasmons

The strong coupling between individual optical emitters and propagating surface plasmons confined to a conducting nanotip make this system act as an ideal interface for quantum networks, through which a stationary qubit and a flying photon (surface plasmon) qubit can be interconverted via a Raman process. This quantum interface paves the way for many essential functions of a quantum network, including sending, receiving, transferring, swapping, and entangling qubits at distributed quantum nodes as well as a deterministic source and an efficient detector of a single-photon. Numerical simulation shows that this scheme is robust against experimental imperfections and has high fidelity. Furthermore, being smaller this interface would significantly facilitate the scalability of quantum computers.

quant-ph↗

arXiv2008

Efficient Long-distance Quantum Communication Using Microtoroidal Resonators

Based on the interaction between a three-level system and a microtoroidal resonator, we present a scheme for long-distance quantum communication in which entanglement generation with near 0.5 success probability and swaps can be implemented by accurate state detection via measuring about 100 photons. With this scheme the average time of successful entanglement distribution over 2500 km with high fidelity can be decreased to only about 30 ms, by 7 orders of magnitude smaller compared with famous Duan-Lukin-Cirac-Zoller (DLCZ) protocol [L.-M. Duan {\it et al.} Nature (London) {\bf414}, 413 (2001)].

quant-ph↗

arXiv2008

Dispersive CQED interactions between matter qubits and bright squeezed light

Dispersive interactions of matter qubits with bright squeezed light in a high-Q cavity is studied. Numerical simulation shows that higher fidelity of operations to obtain a certain phase shift of the pulse through the dispersive light-matter interaction may be reached using bright squeezed light than that using bright coherent light.

quant-ph↗

arXiv2008

The Bound of Entanglement of Superpositions with More Than Two Components

A bipartite quantum state (for two systems in any dimensions) can be decomposed as a superposition of many components. For a superposition of more than two components we prove that there is a bound of the entanglement of the superposition state which can be expressed according to entanglements of its component states. Especially, if the component states are mutually bi-orthogonal, the entanglement of the superposition state can be exactly given in terms of the entanglements of the states being superposed.

quant-ph↗