High-speed large-scale 3D imaging of neuronal activity poses a major challenge in neuroscience. Here, we demonstrate intrinsically simultaneous functional imaging of neuronal activity at single neuron resolution for an entire Caenorhabditis elegans as well as for the whole-brain of larval zebrafish. Our technique captures dynamics of spiking neurons in volumes of ~700 μm x 700 μm x 200 μm at 20 Hz and its simplicity makes it an attractive tool for high-speed volumetric calcium imaging.

As information carriers in quantum computing 1 , photonic qubits have the advantage of undergoing negligible decoherence. However, the absence of any significant photonphoton interaction is problematic for the realization of non-trivial two-qubit gates. One solution is to introduce an effective nonlinearity by measurements resulting in probabilistic gate operations 2,3 . In one-way quantum computation 4-8 , the random quantum measurement error can be overcome by applying a feed-forward technique, such that the future measurement basis depends on earlier measurement results. This technique is crucial for achieving deterministic quantum computation once a cluster state (the highly entangled multiparticle state on which one-way quantum computation is based) is prepared. Here we realize a concatenated scheme of measurement and active feed-forward in a one-way quantum computing experiment. We demonstrate that, for a perfect cluster state and no photon loss, our quantum computation scheme would operate with good fidelity and that our feed-forward components function with very high speed and low error for detected photons. With present technology, the individual computational step (in our case the individual feed-forward cycle) can be operated in less than 150 ns using electro-optical modulators. This is an important result for the

One of the fundamental goals of neuroscience is to understand how external sensory inputs and internal states are represented and processed by neuronal circuits in the nervous system to generate behavior. While in both simple and more complex organisms there is evidence of the existence of discrete anatomically pathways that compute sensory input and generate motor output, there is an increasing understanding that, most sensory functions and behavioral states are represented in a flexible and distributed fashion across large neuronal networks 1, 2 elegans nervous system, such as correlated activity among groups of neurons and their responses to sensory stimuli. This paves the way for future investigations on how sensory information is processed at the level of the whole brain, and for establishing a functional map of C. elegans' nervous system and potentially also in other model organisms. RESULTS Volumetric imaging using WF-TEFOOur approach for volumetric imaging is based on temporal focusing 15-18, 20, 21 .This two-photon excitation scheme allows to independently control the axial and lateral confinement of the excitation area while taking advantage of the high depth penetration and low scattering properties 22, 23 of two-photon excitation. In temporal focusing, the spectrum of a femtosecond laser pulse is spatially dispersed by a grating. The illuminated spot on the grating is imaged via a telescope, consisting of a relay lens and the microscope objective, inside the sample (Fig. 1A). Thereby, the spectral components of the laser pulse overlap in time and space only in the focus region where near-diffraction limited axial confinement of the excitation is achieved leading to high twophoton excitation probability, while wide-field excitation is maintained (see Online Methods for details). Outside of the focal region the pulse is chirped which reduces the two-photon excitation probability. Temporal focusing is compatible with conventional inverted or upright microscopes (Fig. 1A). Using this technique a wide-field two-photon excitation area of ~ 60 × 60 μm with an axial confinement of ~ 1.9 μm is generated (Online Methods) ( Fig. 1B-C).Furthermore, we have implemented a fast detection scheme based on an sCMOS camera coupled to a high-gain image intensifier. This eliminates the common trade-off between acquisition speed and sensitivity when comparing sCMOS and EMCCD cameras. Thereby we could retain the low noise floor of the sCMOS camera while benefiting from the signal enhancement of the intensifier ( Fig. 1D-F).Volumetric imaging is thus performed by scanning in the axial direction only, speeding up the volume acquisition time. For the lateral size described above and an axial range of over 30 μm, our microscope can achieve a volume acquisition rate of ~13Hz. However, due to limitations set by baseline fluorescence and signal to noise ratio of the Ca 2+ -sensor, as well as tolerable expression levels in C. elegans (see Online Methods for details), we performed the imaging at volumetric acquisition speeds of ...

The role and importance of mechanical properties of cells and tissues in cellular function, development as well as disease has widely been acknowledged, however standard techniques currently used to assess them exhibit intrinsic limitations. Recently, a new type of optical elastography, namely Brillouin microscopy, has emerged as a nondestructive, label-and contact-free method which can probe the viscoelastic properties of biological samples with diffraction-limited resolution in 3D. This has led to increased attention amongst the biological and medical research communities, but also to debates about the interpretation and relevance of the measured physical quantities. Here, we review this emerging technology by describing the underlying biophysical principles and discussing the interpretation of Brillouin spectra arising from heterogeneous biological matter. We further elaborate on the technique's limitations as well as its potential for new insights in biology in order to guide interested researchers from various fields.

We report the first experimental generation and characterization of a six-photon Dicke state. The produced state shows a fidelity of F = 0.56 ± 0.02 with respect to an ideal Dicke state and violates a witness detecting genuine six-qubit entanglement by four standard deviations. We confirm characteristic Dicke properties of our resource and demonstrate its versatility by projecting out four-and five-photon Dicke states, as well as four-photon GHZ and W states. We also show that Dicke states have interesting applications in multiparty quantum networking protocols such as opendestination teleportation, telecloning and quantum secret sharing. In this Letter we report the experimental generation and investigation of a variety of multi-photon entangled states. We present a flexible linear-optics setup that can produce four-, five-and six-photon representatives of the important class of Dicke states, as well as four-photon GHZ states. Information is encoded in the polarization degrees of freedom of entangled photons produced by high-order spontaneous parametric down conversion (SPDC). We show that our generated states are genuinely multipartite entangled by using tailormade and experimentally favorable witness tools. These new characterization methods are important in virtue of the non-ideal nature of the six-photon state: although spurious nonlinear processes affect its quality, quantum features can still be observed and characterized. We also highlight the potential for quantum control in large Hilbert spaces by evaluating protocols such as telecloning, open-destination teleportation and quantum secret sharing [11,12,13,14,15].Experiment.- Fig. 1 (a) shows the setup for the generation of the three-excitation six-photon Dicke state |D (3) 6 = 1 √ 20 P |HHHV V V 123456 . Here, |H/V i are horizontal/vertical polarization states of a photon in spatial mode i = 1, .., 6, which encode the logical states of a qubit, while P denotes the sum over all permutations of logical states [16]. In the setup, six photons are probabilistically distributed among the spatial modes by nonpolarizing beamsplitters (BSs): upon detecting one photon in each mode we post-selectively observe |D (3) 6. We use higher-order emissions of a collinear type-II SPDC process for the simultaneous production of three pairs of photons [17]. A Coherent Inc. Verdi V-18 laser is combined with a mode-locked Mira HP Ti:Sa oscillator to reach the energy necessary to observe third-order SPDC emissions. The pulsed-laser output (τ = 200 fs, λ = 810 nm, 76 MHz) is frequency-doubled using a 2 mmthick Lithium triborate (LBO) crystal, resulting in UV pulses of 1.4 W cw-average. To avoid optical damage to the anti-reflection coating of the LBO, we continuously translate it with a step-motor, achieving a very stable source of UV pulses (power and count-rate fluctuations less than 1 − 2% over 30 h). The UV pulses are focused onto a 2 mm-thick β-barium borate (BBO) type-II crystal, cut for collinear down-conversion emission. Dichroic mirrors then separate the down-converted...

We demonstrate a new architecture for an optical entangling gate that is significantly simpler than previous realizations, using partially polarizing beam splitters so that only a single optical mode-matching condition is required. We demonstrate operation of a controlled-z gate in both continuous-wave and pulsed regimes of operation, fully characterizing it in each case using quantum process tomography. We also demonstrate a fully resolving, nondeterministic optical Bell-state analyzer based on this controlled-z gate. This new architecture is ideally suited to guided optics implementations of optical gates.

Heisenberg's uncertainty principle provides a fundamental limitation on an observer's ability to simultaneously predict the outcome when one of two measurements is performed on a quantum system. However, if the observer has access to a particle (stored in a quantum memory) which is entangled with the system, his uncertainty is generally reduced. This effect has recently been quantified by Berta et al. [Nature Physics 6, 659 (2010)] in a new, more general uncertainty relation, formulated in terms of entropies. Using entangled photon pairs, an optical delay line serving as a quantum memory and fast, active feed-forward we experimentally probe the validity of this new relation. The behaviour we find agrees with the predictions of quantum theory and satisfies the new uncertainty relation. In particular, we find lower uncertainties about the measurement outcomes than would be possible without the entangled particle. This shows not only that the reduction in uncertainty enabled by entanglement can be significant in practice, but also demonstrates the use of the inequality to witness entanglement.Consider an experiment in which one of two measurements is made on a quantum system. In general, it is not possible to predict the outcomes of both measurements precisely, which leads to uncertainty relations constraining our ability to do so. Such relations lie at the heart of quantum theory and have profound fundamental and practical consequences. They set fundamental limits on precision technologies such as metrology and lithography, and also served as the intuition behind new types of technologies such as quantum cryptography [1,2].The first relation of this kind was formulated by Heisenberg for the case of position and momentum [3]. Subsequent work by Robertson [4] and Schrödinger [5] generalized this relation to arbitrary pairs of observables. In particular, Robertson showed thatwhere uncertainty is characterized in terms of the standard deviation ∆R for an observable R (and likewise for S) and the right-hand-side (RHS) of the inequality is expressed in terms of the expectation value of the commutator, [R, S] := RS − SR, of the two observables. More recently, driven by information theory, uncertainty relations have been developed in which the uncertainty is quantified using entropy [6,7], rather than the standard deviation. This links uncertainty relations more naturally to classical and quantum information and overcomes some pitfalls of equation (1) pointed out by Deutsch [7]. Most uncertainty relations apply only in the case where the uncertainty is measured for an observer holding only classical information about the system. One such relation, conjectured by Kraus [8] and subsequently proven by Maassen and Uffink [9], states that for any observables R and Swhere H(R) denotes the Shannon entropy [10] of the probability distribution of the outcomes when R is measured and the term 1/c quantifies the complementarity of the observables. For non-degenerate observables, it is defined by c := max r,s | Ψ r |Υ s | 2 , where ...

We demonstrate phase super-resolution in the absence of entangled states. The key insight is to use the inherent time-reversal symmetry of quantum mechanics: our theory shows that it is possible to measure, as opposed to prepare, entangled states. Our approach is robust, requiring only photons that exhibit classical interference: we experimentally demonstrate high-visibility phase super-resolution with three, four, and six photons using a standard laser and photon counters. Our six-photon experiment demonstrates the best phase super-resolution yet reported with high visibility and resolution.Common wisdom holds that entangled states are a necessary resource for many protocols in quantum information. An example is quantum metrology, which promises super-precise measurement, surpassing that possible with classical states of light and matter [1,2]. In the last 20 years quantum metrology schemes have been proposed for improved optical [3][4][5][6][7][8] and matter-wave [9] interferometry, atomic spectroscopy [10], and lithography [11][12][13]. The entangled states in these schemes give rise to phase super-resolution, where the interference oscillation occurs over a phase N-times smaller than one cycle of classical light [14,15] and phase super-sensitivity, a reduction of phase uncertainty.Many quantum metrology schemes are based on pathentangled number states. The canonical example is the noon-state [1], a two-mode state with either N particles in one mode and 0 in the other or vice-versa, i.e., (|N0 +|0N )/ √ 2. A deterministic optical source of path-entangled states is yet to be realised, requiring optical nonlinearities many orders of magnitude larger than those currently possible. However, entangled states can be made non-deterministically using single-photon sources, linear optics, and photon-resolving detectors [16]: leading to a flurry of proposals to generate pathentangled states [17][18][19][20]. While phase super-resolution with two-photons has been demonstrated often since 1990 [21][22][23][24], phase super-resolution was experimentally demonstrated for 3-photon [14] and 4-photon [15] states only recently. As efficient photon sources and photonnumber resolving detectors do not yet exist, all demonstrations to date necessarily used multiphoton coincidence post-selection [25]. Problematically, current photon sources are extremely dim and true photon-number resolving detectors are expensive and uncommon. In this paper we introduce a time-reversal technique that eliminates the need for exotic sources and detectors, achieving high-visibility phase super-resolution with a standard laser and photon detectors.