We present an indirect two-qubit parity meter in planar circuit quantum electrodynamics, realized by discrete interaction with an ancilla and a subsequent projective ancilla measurement with a dedicated, dispersively coupled resonator. Quantum process tomography and successful entanglement by measurement demonstrate that the meter is intrinsically quantum nondemolition. Separate interaction and measurement steps allow the execution of subsequent data-qubit operations in parallel with ancilla measurement, offering time savings over continuous schemes. DOI: 10.1103/PhysRevLett.112.070502 PACS numbers: 03.67.Bg, 03.67.Lx, 42.50.Pq, 85.25.-j Controlling the entanglement between qubits is central to the development of every quantum computing architecture. Early efforts with superconducting quantum circuits relied on quantum interference for this purpose. Programmed sequences of one-and few-qubit gates fitting within qubit coherence times have allowed the generation of two-and three-qubit entanglement [1][2][3][4] and the implementation of elementary quantum algorithms [5][6][7][8][9] and games [10].Recently, focus has shifted toward generating and preserving entanglement by nondemolition measurement of multiqubit observables and their use in feedback loops as required for quantum error correction [11]. Of particular interest is the parity measurement [12][13][14] that discriminates between states in a multiqubit register with even or odd total excitation number. Parity measurement on four data qubits at the corners of every square tile on a lattice is needed to realize surface codes, offering the highest faulttolerance thresholds to date [15,16].A convenient approach to implementing a parity measurement is a two-step indirect scheme involving coherent interaction of the data qubits with an ancillary qubit and subsequent strong measurement of this ancilla. To date, indirect four-qubit parity measurements have been achieved only in trapped-ion systems [17]. In the solid state, parity measurement using an ancillary electron spin has been used to generate probabilistic entanglement between two nuclear spins in nitrogen-vacancy centers in diamond [18]. More recently, parity measurement of two transmon qubits using a dispersively coupled 3D cavity has been used in a digital feedback loop to generate entanglement deterministically [19]. An important next step is the realization of parity measurements in an architecture amenable to surface coding.In this Letter, we present an ancilla-based two-qubit parity measurement in a planar circuit QED (cQED) architecture [20]. Tomographic characterization shows that dephasing within even and odd parity subspaces is due to intrinsic qubit decoherence during interaction and measurement steps, making the parity meter intrinsically quantum nondemolition (QND). As a further demonstration of this nondemolition character, we generate entanglement by parity measurement on a maximal superposition state. Performing all tomographic data-qubit operations after the ancilla measurement, we achi...

Tailored nanostructures provide at-will control over the properties of light, with applications in imaging and spectroscopy. Active photonics can further open new avenues in remote monitoring, virtual or augmented reality and time-resolved sensing. Nanomaterials with χ(2) nonlinearities achieve highest switching speeds. Current demonstrations typically require a trade-off: they either rely on traditional χ(2) materials, which have low non-linearities, or on application-specific quantum well heterostructures that exhibit a high χ(2) in a narrow band. Here, we show that a thin film of organic electro-optic molecules JRD1 in polymethylmethacrylate combines desired merits for active free-space optics: broadband record-high nonlinearity (10-100 times higher than traditional materials at wavelengths 1100-1600 nm), a custom-tailored nonlinear tensor at the nanoscale, and engineered optical and electronic responses. We demonstrate a tuning of optical resonances by Δλ = 11 nm at DC voltages and a modulation of the transmitted intensity up to 40%, at speeds up to 50 MHz. We realize 2 × 2 single- and 1 × 5 multi-color spatial light modulators. We demonstrate their potential for imaging and remote sensing. The compatibility with compact laser diodes, the achieved millimeter size and the low power consumption are further key features for laser ranging or reconfigurable optics.

Electro-optic modulators are essential for sensing, metrology and telecommunications. Most target fiber applications. Instead, metasurface-based architectures that modulate free-space light at gigahertz (GHz) speeds can boost flat optics technology by microwave electronics for active optics, diffractive computing or optoelectronic control. Current realizations are bulky or have low modulation efficiencies. Here, we demonstrate a hybrid silicon-organic metasurface platform that leverages Mie resonances for efficient electro-optic modulation at GHz speeds. We exploit quasi bound states in the continuum (BIC) that provide narrow linewidth (Q = 550 at $${\lambda }_{{{{{{{{\rm{res}}}}}}}}}=1594$$ λ res = 1594  nm), light confinement to the non-linear material, tunability by design and voltage and GHz-speed electrodes. Key to the achieved modulation of $$\frac{{{\Delta }}T}{{T}_{\max }}=67 \%$$ Δ T T max = 67 % are molecules with r33 = 100 pm/V and optical field optimization for low-loss. We demonstrate DC tuning of the resonant frequency of quasi-BIC by $${{\Delta }}{\lambda }_{{{{{{{{\rm{res}}}}}}}}}=$$ Δ λ res =  11 nm, surpassing its linewidth, and modulation up to 5 GHz (fEO,−3dB = 3 GHz). Guided mode resonances tune by $${{\Delta }}{\lambda }_{{{{{{{{\rm{res}}}}}}}}}=$$ Δ λ res =  20 nm. Our hybrid platform may incorporate free-space nanostructures of any geometry or material, by application of the active layer post-fabrication.

Free-standing nanofins or pillar meta-atoms are the most common constituent building blocks in metalenses and metasurfaces in general. Here, we present an alternative metasurface geometry based on high aspect ratio via-holes. We design and characterize metalenses comprising ultradeep via-holes in 5 μm thick free-standing silicon membranes with hole aspect ratios approaching 30:1. These metalenses focus incident infrared light into a diffraction-limited spot. Instead of shaping the metasurface optical phase profile alone, we engineer both transmitted phase and amplitude profiles simultaneously by inversedesigning the lens effective index profile. This approach improves the impedance match between the incident and transmitted waves, thereby increasing the focusing efficiency. The holey platform increases the accessible aspect ratio of optical nanostructures without sacrificing mechanical robustness. The high nanostructure aspect ratio also increases the chromatic group delay range attainable, paving the way for a generation of high aspect ratio ruggedized flat optics, including large-area broadband achromatic metalenses.

Abstract:We have investigated the transport of light through slabs that both scatter and strongly absorb, a situation that occurs in diverse application fields ranging from biomedical optics, powder technology, to solid-state lighting. In particular, we study the transport of light in the visible wavelength range between 420 and 700 nm through silicone plates filled with YAG:Ce 3+ phosphor particles, that even re-emit absorbed light at different wavelengths. We measure the total transmission, the total reflection, and the ballistic transmission of light through these plates. We obtain average single particle properties namely the scattering cross-section σ s , the absorption cross-section σ a , and the anisotropy factor µ using an analytical approach, namely the P3 approximation to the radiative transfer equation. We verify the extracted transport parameters using Monte-Carlo simulations of the light transport. Our approach fully describes the light propagation in phosphor diffuser plates that are used in white LEDs and that reveal a strong absorption (L/l a > 1) up to L/l a = 4, where L is the slab thickness, l a is the absorption mean free path. In contrast, the widely used diffusion theory fails to describe this parameter range. Our approach is a suitable analytical tool for industry, since it provides a fast yet accurate determination of key transport parameters, and since it introduces predictive power into the design process of white light emitting diodes. 8190-8204 (2014). 30. To be sure, in a scattering system the degree of scattering is given by L/ s rather than L/ t r . Since in the vast majority of scattering systems the transport mean free paths exceeds the scattering mean free path ( t r ≥ s ) due to predominantly forward scattering [34], we consider our characterization to be on the safe side. 31. S. Chandrasekhar, Radiative transfer (Dover, New York NY, 1960). 32. M. Kaveh, Analogies in optics and micro electronics (Springer, Netherlands, 1991) 33.