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A Quantum Image Watermarking Scheme Based on Two-Bit Superposition
摘要： Quantum watermarking technology protects copyright by embedding an invisible quantum signal in quantum multimedia data. This paper proposes a two-bit superposition method which embeds a watermark image (or secret information) into a carrier image. Firstly, the bit-plane is used to encrypt the watermark image. At the same time, the quantum expansion method is used to extend the watermark image to the same size with the carrier image, and then the image is encrypted through the Fibonacci scramble method again. Secondly, the first proposed method is the two bits of the watermark image which is embedded into the carrier image in accordance with the order of the high and lowest qubit, and the second proposed method which is the high bit of the watermark image is embedded to the lowest bit. Then the lowest bit of the watermark image is embedded in carrier image. Third, the watermark image is extracted through 1-CNOT and swap gates, and the watermark image is restored by inverse Fibonacci scramble, inverse expansion method and inverse bit-plane scramble method. Finally, for the validation of the proposed scheme, the signal-to-noise ratio (PSNR), the image histogram and the robustness of the two watermarking methods are analyzed.
关键词： Fibonacci scramble,Swap gates,Superposition,Robustness,Bit-plane scramble
更新于2025-09-23 15:23:52
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Engineering bilinear mode coupling in circuit QED: Theory and experiment
摘要： Photonic states of high-Q superconducting microwave cavities controlled by superconducting transmon ancillas provide a platform for encoding and manipulating quantum information. A key challenge in scaling up the platform towards practical quantum computation is the requirement to communicate on demand the quantum information stored in the cavities. It has been recently demonstrated that a tunable bilinear interaction between two cavity modes can be realized by coupling the modes to a bichromatically driven superconducting transmon ancilla, which allows swapping and interfering the multiphoton states stored in the cavity modes [Gao et al., Phys. Rev. X 8, 021073 (2018)]. Here we explore both theoretically and experimentally the regime of relatively strong drives on the ancilla needed to achieve fast SWAP gates but which can also lead to undesired nonperturbative effects that lower the SWAP fidelity. We develop a theoretical formalism based on linear response theory that allows one to calculate the rate of ancilla-induced interaction, decay, and frequency shift of the cavity modes in terms of a susceptibility matrix. We go beyond the usual perturbative treatment of the drives by using Floquet theory, and find that the interference of the two drives can strongly alter the system dynamics even in the regime where the standard rotating wave approximation applies. The drive-induced ac Stark shift on the ancilla depends nontrivially on the drive and ancilla parameters which in turn modify the strength of the engineered interaction. We identify two major sources of infidelity due to ancilla decoherence. (i) Ancilla dissipation and dephasing lead to incoherent hopping among Floquet states which occurs even when the ancilla is at zero temperature; this hopping results in a sudden change of the SWAP rate, thereby decohering the SWAP operation. (ii) The cavity modes inherit finite decay from the relatively lossy ancilla through the inverse Purcell effect; the effect becomes particularly strong when the ac Stark shift pushes certain ancilla transition frequencies to the vicinity of the cavity mode frequencies. The theoretical predictions agree quantitatively with the experimental results, paving the way for using the developed theory for optimizing future experiments and architecture designs.
关键词： decoherence,transmon ancilla,superconducting cavities,ac Stark shift,quantum information,circuit QED,inverse Purcell effect,bilinear mode coupling,SWAP gates,Floquet theory
更新于2025-09-23 15:23:52
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Coherent transfer of quantum information in a silicon double quantum dot using resonant SWAP gates
摘要： Spin-based quantum processors in silicon quantum dots offer high-fidelity single and two-qubit operation. Recently multi-qubit devices have been realized; however, many-qubit demonstrations remain elusive, partly due to the limited qubit-to-qubit connectivity. These problems can be overcome by using SWAP gates, which are challenging to implement in devices having large magnetic field gradients. Here we use a primitive SWAP gate to transfer spin eigenstates in 100 ns with a fidelity of F(p)SWAP = 98%. By swapping eigenstates we are able to demonstrate a technique for reading out and initializing the state of a double quantum dot without shuttling charges through the quantum dot. We then show that the SWAP gate can transfer arbitrary two-qubit product states in 300 ns with a fidelity of F(c)SWAP = 84%. This work sets the stage for many-qubit experiments in silicon quantum dots.
关键词： silicon quantum dots,quantum processors,SWAP gates,spin eigenstates,quantum information
更新于2025-09-11 14:15:04
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Faithful Entanglement Purification for High-Capacity Quantum Communication with Two-Photon Four-Qubit Systems
摘要： As the hyperentanglement of photon systems presents lots of unique opportunities in high-capacity quantum networking, the hyperentanglement purification protocol (hyper-EPP) becomes a vital project work and the quality of its accomplishment attracts considerable attention recently. Here we present the first theoretical scheme of faithful hyper-EPP for nonlocal two-photon systems in two degrees of freedom (DOFs) by constructing several fidelity-robust quantum circuits for hyper-encoded photons. With this faithful hyper-EPP, the bit-flip errors in both the polarization and spatial-mode DOFs can be efficiently corrected and the maximal hyperentanglement in two DOFs could in principle be achieved by performing the hyper-EPP multiple rounds. Moreover, the fidelity-robust quantum circuits, parity-check quantum nondemolition detectors, and SWAP gates make this hyper-EPP works faithfully as the errors coming from practical scattering, in these quantum circuits, are converted into a detectable failure rather than infidelity. Furthermore, this hyper-EPP can be directly extended to purify photon systems entangled in single polarization or spatial-mode DOF and that hyperentangled in polarization and multiple-spatial-mode DOFs.
关键词： hyperentanglement,SWAP gates,quantum communication,quantum circuits,entanglement purification
更新于2025-09-11 14:15:04