Experimental classical entanglement in a 16 acoustic qubit-analogue

The possibility of achieving and controlling scalable classically entangled, i.e., inseparable, multipartite states, would fundamentally challenge the advantages of quantum systems in harnessing the power of complexity in information science. Here, we investigate experimentally the extent of classical entanglement in a $$16$$ 16 acoustic qubit-analogue platform. The acoustic qubit-analogue, a.k.a., logical phi-bit, results from the spectral partitioning of the nonlinear acoustic field of externally driven coupled waveguides. Each logical phi-bit is a two-level subsystem characterized by two independently measurable phases. The phi-bits are co-located within the same physical space enabling distance independent interactions. We chose a vector state representation of the $$16$$ 16 -phi-bit system which lies in a $${2}^{16}$$ 2 16 -dimensional Hilbert space. The calculation of the entropy of entanglement demonstrates the possibility of achieving inseparability of the vector state and of navigating the corresponding Hilbert space. This work suggests a new direction in harnessing the complexity of classical inseparability in information science.

Artificial gauge induced dispersionless coupling for broadband photonic waveguide integration

Coupling among waveguides plays an important role in photonic integration, while it usually suffers from large wavelength dispersion and structural sensitivity that brings difficulties in broadband and robust photonic chip devices. Here, we report a new strategy of dispersion engineering of coupled waveguides by artificial gauge field (AGF) with curved trajectories, which gives rise to a dispersionless broadband coupler function in high-density silicon waveguides (waveguide pitch <λ/2). It is found that the artificial gauge field can generate an inverse dispersion to compensate for the dispersion of conventional waveguide coupling. As such, the coupling between the waveguides can be stable in a broad bandwidth. Based on this design, we demonstrate compact directional and 3dB couplers that show broadband dispersionless coupling of light with wavelength from 1400 to 1650 nm, which also exhibit robustness to considerably large structural variations ~150 nm (75% structural deviation). Furthermore, using the AGF coupler as the building block, we significantly demonstrate a three-level-cascaded waveguide network to route the broadband light to the desired ports, showing a tremendous advantage over the conventional counterparts. Our work exploits the artificial gauge field to integrated photonics and demonstrates the possibility of massive, broadband, robust and dense photonic integrations.

Quantum entanglement and statistics of photons on a beam splitter in the form of coupled waveguides

It is well known that a beam splitter (BS) can be used as a source of photon quantum entanglement. This is due to the fact that the statistics of photons changes at the output ports of the BS. Usually, quantum entanglement and photon statistics take into account the constancy of the reflection coefficient R or the transmission coefficient T of the BS, where $$R + T = 1$$ R + T = 1 . It has recently been shown that if BS is used in the form of coupled waveguides, the coefficients R and T will depend on the photon frequencies. In this paper, it is shown that the quantum entanglement and statistics of photons at the output ports of a BS can change significantly if a BS is used in the form of coupled waveguides, where the coefficients R and T are frequency-dependent.