arXiv subjects

Fang-Fang Du

Publications and source records attributed to Fang-Fang Du.

13 recordsLinked to original sources

arXiv2025

Heralded deterministic Knill-Laflamme-Milburn entanglement generation for solid-state emitters via waveguide-assisted photon scattering

The realization of quantum networks that exploit multiqubit entanglement opens avenues for transformative applications in the realm of quantum communication. In the paper, we present a set of heralded deterministic protocols designed for the generation of two-qubit, three-qubit, and $N$-qubit Knill-Laflamme-Milburn (KLM) states by the photon scattering property in one-dimensional waveguide-emitter system. In each protocol, the auxiliary single photon functions as a universal interface to bridge all stationary qubits. Our proposed protocols allow for the conversion of irregular scattering incidents occasioned by nonideal coupling and frequency detuning into detectable events by triggering the detectors, which mean that our protocols for the generation of arbitrary KLM states with the predictive operational character and high fidelities. Owing to the significant breakthroughs in the integration of quantum emitters with nanophotonic waveguides, our protocolfs possess ideal features that position them as the promising candidate for deployment in long-range multiqubit quantum networks systems.

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arXiv2025

Computing-heightened low-cost high-dimensional controlled-SUM gates

Qudit-based quantum gates offer several advantages over qubit-based counterparts, such as higher information density, the ability to address more complex problems, and richer quantum operations. In this paper, we present three realistic protocols for implementing a 4$\times$4-dimensional (16D) two-qudit controlled-SUM (CSUM) gate, where the 4D control qudit and 4D target qudit are encoded in the polarization degree of freedom (DoF) and spatial DoF of two photons, respectively. The first protocol is implemented exclusively using linear optical elements without auxiliary resources, making it feasible with current optical technologies and achieving an efficiency of 1/9. The second protocol utilizes photon scattering by a microcavity-quantum-dot system, enabling the 16D CSUM gate to operate deterministically without postselection. The third protocol introduces an error-heralded mechanism based on the second protocol, theoretically achieving unity fidelity. Moreover, all protocols operate without ancillary photons, offering the advantages of compact circuits and low cost while further promoting the development of high-dimensional quantum computation.

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arXiv2025

Heralded qudit-based high-dimensional entanglement generation for hybrid photon-emitter system by waveguide-mediated scattering

Quantum entanglement systems based on qudits dilate high-dimensional (HD) state spaces and enhance resistance to loss in quantum information processing (QIP). To fully exploit this potential, effective schemes for generating HD entanglement are crucial. In this paper, we propose a flexible heralded scheme generating random 4D two-qudit maximal entanglement for hybrid photon-emitter system by entering different input ports. This approach can be further extended to prepare 4D n-qudit (n is greater than or equal 3) maximal entanglement utilizing the 4D single-qudit Z^m (m=1,2,3) gate for the first qudit and X^m gate for the other qudits (except the second qudit). For the hybrid system, the first 4D qudit is encoded on the hybrid polarization-path states of a flying photon, while the second and subsequent 4D qudits are represented by two stationary emitters coupled to respective 1D waveguide. The qudit-encoded hybrid HD entanglement offers advantages over economizing quantum resource without any auxiliary qudits, and obtaining robust fidelities of various HD entanglement by the error-detected mechanism of the emitter-waveguide systems. Moreover, the proposed protocol can be spread to generate dD n-qudit (d is greater than or equal 2^(p+1), n, p=2,3,...) entangled states, further broadening its applicability in HD QIP.

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arXiv2024

A Computation-Enhanced High-Dimensional Quantum Gate for Silicon-Vacancy Spins

Qudit-based quantum gates in high-dimensional Hilbert space can provide a viable route towards effectively accelerating the speed of quantum computing and performing complex quantum logic operations. In the paper, we propose a 2-qudit $4\times4$-dimensional controlled-not (CNOT) gate for four silicon-vacancy spins, in which the first two electron-spin states in silicon-vacancy centers are encoded as the control qudits, and the other ones as the target qudits. The proposed protocol is implemented with assistance of an ancillary photon that serves as a common-data bus linking four motionless silicon-vacancy spins placed in four independent single-sided optical nanocavities. Moreover, the CNOT gate works in a deterministic manner by performing the relational feed-forward operations corresponding to the diverse outcomes of the single-photon detectors to be directed against the ancillary photon. Further, it can be potentially generalized to other solid-state quantum system. Under current technological conditions, both the efficiency and fidelity of the 2-qudit CNOT gate are high.

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arXiv2024

Kerr-effect-based quantum logical gates in decoherence-free subspace

The decoherence effect caused by the coupling between the system and the environment undoubtedly leads to the errors in efficient implementations of two (or three) qubit logical gates in quantum information processing. Fortunately, decoherence-free subspace (DFS) introduced can effectively decrease the influence of decoherence effect. In this paper, we propose some schemes for setting up a family of quantum control gates, including controlled-NOT (CNOT), Toffoli, and Fredkin gates for two or three logical qubits by means of cross-Kerr nonlinearities in DFS. These three logical gates require neither complicated quantum computational circuits nor auxiliary photons (or entangled states). The success probabilities of three logical gates are approximate 1 by performing the corresponding classical feed-forward operations based on the different measuring results of the X-homodyne detectors, and their fidelities are robust against the photon loss with the current technology. The proposed logical gates rely on only simple linear-optics elements, available single-qubit operations, and mature measurement methods, making our proposed gates be feasible and efficient in practical applications.

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arXiv2022

Refined quantum gates for $Λ$-type atom-photon hybrid systems

High-efficiency quantum information processing is equivalent to the fewest quantum resources and the simplest operations by means of logic qubit gates. Based on the reflection geometry of a single photon interacting with a three-level $Λ$-typle atom-cavity system, we present some refined protocols for realizing controlled-not (CNOT), Fredkin, and Toffoli gates on hybrid systems. The first control qubit of our gates is encoded on a flying photon, and the rest qubits are encoded on the atoms in optical cavity. Moreover, these quantum gates can be extended to the optimal synthesis of multi-qubit CNOT, Fredkin and Toffoli gates with O(n) optical elements without auxiliary photons or atoms. Further, the simplest single-qubit operations are applied to the photon only, which make these logic gates experimentally feasible with current technology.

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arXiv2022

Deterministic and complete hyperentangled Bell states analysis assisted by frequency and time interval degrees of freedom

Hyperentangled Bell states analysis (HBSA) is an essential building block for certain hyper-parallel quantum information processing. We propose a complete and deterministic HBSA scheme encoded in spatial and polarization degrees of freedom (DOFs) of two-photon system assisted by a fixed frequency-based entanglement and a time interval DOF. The parity information the spatial-based and polarization-based hyper-entanglement can be distinguished by the distinct time intervals of the photon pairs, and the phase information can be distinguished by the detection signature. Compared with previous schemes, the number of the auxiliary entanglements is reduced from two to one by introducing time interval DOF. Moreover, the additional frequency and time interval DOFs suffer less from the collective channel noise.

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arXiv2022

Complete hyperentangled Bell states analysis for polarization-spatial-time-bin degrees of freedom with unity fidelity

Hyperentangled states can outperform their classical counterparts on solving certain tasks. Here we present a simplified scheme for completely distinguishing two-photon hyperentangled Bell states in polarization, spatial, and time-bin degrees of freedom (DOFs). Unity fidelity can be achieved in principle without strong couple limitation between photon and quantum dot (QD), and the incomplete and imperfect QD-cavity interactions are prevented by single-photon detectors. In addition, auxiliary photons or DOFs are not required in our scheme. The necessary linear optical elements are fewer than the parity-check-based one.

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arXiv2015

Systematic entanglement concentration for unknown less-entangled three-photon W states

We present a systematic entanglement concentration protocol (ECP) for an arbitrary unknown less-entangled three-photon W state, resorting to the optical property of the quantum-dot spins inside one-sided optical microcavities. In our ECP, the parties obtain not only some three-photon systems in the partially entangled with two unknown parameters when one of the parties picks up the robust odd-parity instance with the parity-check gate (PCG) on his two photons, but also some entangled two-photon systems by keeping the even-parity instance in the first step. By exploiting the above three-photon and two-photon systems with the same parameters as the resource for the second step of our ECP, the parties can obtain a standard three-photon W state by keeping the robust odd-parity instance. Meanwhile, the systems in the even-parity instance can be used as the resource in the next round of our ECP. The success probability of our ECP is largely increased by iteration of the ECP process. As it does require that all the coefficients are unknown for the parties, our ECP maybe have good applications in quantum communication network in future.

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arXiv2014

Two-step hyperentanglement purification with the quantum-state-joining method

Hyperentanglement is a promising resource in quantum information processing, especially for increasing the channel capacity of long-distance quantum communication. Hyperentanglement purification is an important method to obtain high-fidelity nonlocal hyperentangled states from mixed hyperentangled states in a long-distance quantum communication process with noisy channels. Here, we present a two-step hyperentanglement purification protocol for nonlocal mixed hyperentangled states with polarization bit-flip errors and spatial-mode phase-flip errors, resorting to polarization-spatial phase-check quantum nondemolition detectors and the quantum-state-joining method (QSJM). With QSJM, the protocol can preserve the states that are discarded in the previous hyperentanglement purification protocols. It has the advantage of a high efficiency, and it is useful for improving the entanglement of photon systems with several degrees of freedom in long-distance high-capacity quantum communication.

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arXiv2013

Hyperentanglement concentration for two-photon four-qubit systems with linear optics

Hyperentanglement, defined as the entanglement in several degrees of freedom (DOFs) of a quantum system, has attracted much attention recently. Here we investigate the possibility of concentrating the two-photon four-qubit systems in partially hyperentangled states in both the spatial mode and the polarization DOFs with linear optics. We first introduce our parameter-splitting method to concentrate the systems in the partially hyperentangled states with known parameters, including partially hyperentangled Bell states and cluster states. Subsequently, we present another two nonlocal hyperentanglement concentration protocols (hyper-ECPs) for the systems in partially hyperentangled unknown states, resorting to the Schmidt projection method. It will be shown that our parameter-splitting method is very efficient for the concentration of the quantum systems in partially entangled states with known parameters, resorting to linear-optical elements only. All these four hyper-ECPs are feasible with current technology and they may be useful in long-distance quantum communication based on hyperentanglement as they require only linear optical elements.

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arXiv2012

Single-photon-assisted entanglement concentration of a multi-photon system in a partially entangled W state with weak cross-Kerr nonlinearity

We propose a nonlocal entanglement concentration protocol (ECP) for $N$-photon systems in a partially entangled W state, resorting to some ancillary single photons and the parity-check measurement based on cross-Kerr nonlinearity. One party in quantum communication first performs a parity-check measurement on her photon in an $N$-photon system and an ancillary photon, and then she picks up the even-parity instance for obtaining the standard W state. When she obtains an odd-parity instance, the system is in a less-entanglement state and it is the resource in the next round of entanglement concentration. By iterating the entanglement concentration process several times, the present ECP has the total success probability approaching to the limit in theory. The present ECP has the advantage of a high success probability. Moreover, the present ECP requires only the $N$-photon system itself and some ancillary single photons, not two copies of the systems, which decreases the difficulty of its implementation largely in experiment. It maybe have good applications in quantum communication in future.

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arXiv2011

High-capacity quantum secure direct communication based on quantum hyperdense coding with hyperentanglement

We present a quantum hyperdense coding protocol with hyperentanglement in polarization and spatial-mode degrees of freedom of photons first and then give the details for a quantum secure direct communication (QSDC) protocol based on this quantum hyperdense coding protocol. This QSDC protocol has the advantage of having a higher capacity than the quantum communication protocols with a qubit system. Compared with the QSDC protocol based on superdense coding with $d$-dimensional systems, this QSDC protocol is more feasible as the preparation of a high-dimension quantum system is more difficult than that of a two-level quantum system at present.

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