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We present a novel optical beam steering technique for fiber to free-space to fiber-coupling schemes on optical breadboards, which is based on a glass plate and a pair of glass wedges. Our approach permits much finer adjustments of the beam direction and position when compared to conventional beam steering techniques that use adjusting elements of the same mechanical precision. This results in a much increased precision, accuracy, and stability. Furthermore, the presence of a beam steering element in proximity to the fiber coupler allows a great simplification of the design of this element which is typically considered as the most complex and sensitive element on an optical fiber breadboard. Overall, a beam steering precision of better than $$5\,\upmu $$rad and $$5\,\upmu $$m is demonstrated, resulting in a resolution in coupling efficiency of 0.1%. Likewise, we demonstrate a fiber-to-fiber-coupling efficiency of more than 89.8%, with a stability of 0.2% in a stable temperature environment and 2% fluctuations over a temperature range from 10 to 40 °C over a measurement time of 14 h. Finally, we observe no non-reversible change in the coupling efficiency after performing a series of tests over large temperature variations ($$\varDelta T > 30$$ K). This technique can find direct application in proposed missions for quantum experiments in space (Bongs et al. in STE-QUEST space–time explorer and quantum equivalence principle space test, Technical report STE-QUEST, European Space Agency, 2013; Kaltenbaek et al. in EPJ Quantum Technol 3(1):5, 2016; Carraz et al. in Microgravity Sci Technol 26:139, 2014), e.g., in space-based quantum sensing, where precisely controlled laser light is used to cool and manipulate atoms, or in inter-satellite quantum key distribution.

We present the theoretical analysis of a novel optical beam steering technique (OBST) for fiber to free-space to fiber coupling schemes on optical breadboards. This technique uses glass wedges and plates to correct misalignments in the position and angle of beams on the breadboard. It can be used in any application where stable and robust coupling of light from an input to an output fiber is required, such as laser distribution boards for cold atom experiments in space. We examine the optical performance in terms of coupling efficiency (CE) for a number of different OBST systems and compare the results. Coupling efficiencies above 95% and positional and angular resolution of smaller than 5 μm and 5 μrad can be achieved using this technology.

We study the hyperfine spectrum of atoms of $^{87}$Rb dressed by a radio-frequency field, and present experimental results in three different situations: freely falling atoms, atoms trapped in an optical dipole trap and atoms in an adiabatic radio-frequency dressed shell trap. In all cases, we observe several resonant side bands spaced (in frequency) at intervals equal to the dressing frequency, corresponding to transitions enabled by the dressing field. We theoretically explain the main features of the microwave spectrum, using a semi-classical model in the low field limit and the Rotating Wave Approximation for alkali-like species in general and $^{87}$Rb atoms in particular. As a proof of concept, we demonstrate how the spectral signal of a dressed atomic ensemble enables an accurate determination of the dressing configuration and the probing microwave field., 17 pages, 14 figures, 3 tables

Some of the most sensitive and precise measurements to date are based on matterwave interferometry with freely falling atomic clouds. Examples include high-precision measurements of inertia, gravity and rotation. In order to achieve these very high sensitivities, the interrogation time has to be very long and consequently the experimental apparatus has to be very tall, in some cases reaching ten or even one hundred meters. Cancelling gravitational acceleration, e.g. in atomtronic circuits6,7 and matterwave guides, will result in compact devices having much extended interrogation times and thus much increased sensitivity both for fundamental and practical measurements. In this letter, we demonstrate extremely smooth and controllable matterwave guides by transporting Bose-Einstein condensates (BEC) over macroscopic distances: We use a novel neutral-atom accelerator ring to bring BECs to very high speeds (16x their velocity of sound) and transport them in a magnetic matterwave guide for 15 cm whilst fully preserving their internal coherence. The high angular momentum of more than 40000h per atom gives access to the higher Landau levels of quantum Hall states. The hypersonic velocities combined with our ability to control the potentials with pico-Kelvin precision open new perspectives in the study of superfluidity and give rise to new regimes of tunnelling and transport. Coherent matterwave guides are expected to enable interaction times of several seconds in highly compact devices. These developments will result in portable guided-atom interferometers for applications such as inertial navigation and gravity mapping., Comment: 11 pages, 3 figures

We discuss a scheme to implement a gyroscopic atom sensor with magnetically trapped ultra-cold atoms. Unlike standard light or matter wave Sagnac interferometers no free wave propagation is used. Interferometer operation is controlled only with static, radio-frequency and microwave magnetic fields, which removes the need for interferometric stability of optical laser beams. Due to the confinement of atoms, the scheme may allow the construction of small scale portable sensors. We discuss the main elements of the scheme and report on recent results and efforts towards its experimental realization.

We demonstrate quantum walks of correlated photons in a 2D network of directly laser written waveguides coupled in a 'swiss cross' arrangement. The correlated detection events show high-visibility quantum interference and unique composite behaviour: strong correlation and independence of the quantum walkers, between and within the planes of the cross. Violations of a classically defined inequality, for photons injected in the same plane and in orthogonal planes, reveal non-classical behaviour in a non-planar structure., 5 pages, 5 figures

Multiphoton quantum walks in integrated optics comprise an attractive controlled quantum system, that can mimic less readily accessible quantum systems and exhibit behavior that cannot in general be accurately replicated by classical light without an exponential overhead in resources. The ability to observe the time evolution of such systems is important for characterizing multiparticle quantum dynamics—notably this includes the effects of boundary conditions for walks in spaces of finite size. Here we demonstrate the coherent evolution of quantum walks of two indistinguishable photons using planar arrays of 21 evanescently coupled waveguides fabricated in silicon oxynitride technology. We compare three time evolutions, that follow closely a model assuming unitary evolution, corresponding to three different lengths of the array—in each case we observe quantum interference features that violate classical predictions. The longest array includes reflecting boundary conditions

Quantum mechanics defines two classes of particles-bosons and fermions-whose exchange statistics fundamentally dictate quantum dynamics. Here we develop a scheme that uses entanglement to directly observe the correlated detection statistics of any number of fermions in any physical process. This approach relies on sending each of the entangled particles through identical copies of the process and by controlling a single phase parameter in the entangled state, the correlated detection statistics can be continuously tuned between bosonic and fermionic statistics. We implement this scheme via two entangled photons shared across the polarisation modes of a single photonic chip to directly mimic the fermion, boson and intermediate behaviour of two-particles undergoing a continuous time quantum walk. The ability to simulate fermions with photons is likely to have applications for verifying boson scattering and for observing particle correlations in analogue simulation using any physical platform that can prepare the entangled state prescribed here.

Quantum information science aims to harness uniquely quantum mechanical properties to enhance measurement and information technologies, and to explore fundamental aspects of quantum physics. Of the various approaches to quantum computing [1], photons are particularly appealing for their low-noise properties and ease of manipulation at the single qubit level [2,3]. Encoding quantum information in photons is also an appealing approach to quantum communication, metrology (eg. [4]), measurement (eg. [5]) and other quantum technologies [6]. However, the implementation of optical quantum circuits with bulk optics has reached practical limits. We have developed an integrated waveguide approach to photonic quantum circuits for high performance, miniaturization and scalability [7]. Here we report high-fidelity silica-on-silicon integrated optical realizations of key quantum photonic circuits, including two-photon quantum interference and a controlled-NOT logic gate [8]. We have demonstrated controlled manipulation of up to four photons on-chip, including highfidelity single qubit operations, using a lithographically patterned resistive phase shifter [9]. We have used this architecture to implement a small-scale compiled version of Shor's quantum factoring algorithm [10], demonstrated heralded generation of tunable four photon entangled states from a six photon input [11], a reconfigurable two-qubit circuit [12], and combined waveguide photonic circuits with superconducting single photon detectors [13]. We describe complex quantum interference behavior in multi-mode interference devices with up to eight inputs and outputs [14], and quantum walks of correlated particles in arrays of coupled waveguides [15]. Finally, we give an overview of our recent work on fundamental aspects of quantum measurement [16,17] and diamond [18,19] and nonlinear [20,21] photon sources.

A Correlated Quantum Walk Random walks are powerful tools for modeling statistical events. The analogous quantum walk involves particles tunneling between available sites. Peruzzo et al. (p. 1500 ; see the Perspective by Hillery ) now report on the quantum walk of a correlated pair of photons propagating through a coupled waveguide array. The output pattern resulting from the injection of two correlated photons possess quantum features, indicating that the photons retain their correlations as they walk randomly through the waveguide array, allowing scale-up and parallel searches over many possible paths.

New components are required to take full advantage of the integrated photonic architecture for Quantum Information science. We demonstrate quantum interference in MMI couplers and two-particle quantum walks in coupled waveguides, showing unique quantum behaviour.

We present two novel matter-wave Sagnac interferometers based on ring- shaped time-averaged adiabatic potentials (TAAP). For both the atoms are put into a superposition of two different spin states and manipulated independently using elliptically polarized rf-fields. In the first interferometer the atoms are accelerated by spin-state-dependent forces and then travel around the ring in a matter-wave guide. In the second one the atoms are fully trapped during the entire interferometric sequence and are moved around the ring in two spin-state-dependent "buckets". Corrections to the ideal Sagnac phase are investigated for both cases. We experimentally demonstrate the key atom-optical elements of the interferometer such as the independent manipulation of two different spin states in the ring-shaped potentials under identical experimental conditions., 21+8 pages, 9 figures, 3 appendices

Optical quantum technologies require new photonic components to exploit integrated architecture. We demonstrate quantum interference in MMI couplers and coupled waveguides that implement two-particle quantum walks, showing unique quantum behaviour.

Quantum information science has shown that harnessing quantum mechanical effects can dramatically improve performance for certain tasks in communication, computation and measurement. Of the various physical systems being pursued, single particles of light - photons - are often the logical choice [1]. In addition to single photon sources and detectors, photonic quantum technologies will rely on sophisticated optical circuits [2]. Recently we reported the implementation of quantum optic integrated circuits, which not only dramatically reduces the footprint of quantum circuits, but allows unprecedented stability and higher performance. We demonstrated silica on silicon circuits that implement key components for quantum information, including CNOT gates [3] and single-qubit operations [4]. These components show promising progresses toward fault tolerance operation [5]. We also used integrated waveguides to implement a circuit that performs a compiled version of Shor's quantum algorithm [6] to factorize 15. Here we report the demonstration of circuits that extend the capabilities of the components already demonstrated, to take full advantage of the integrated optics architecture.

New photonic components are required to exploit the integrated architecture for Quantum Information science. We demonstrate quantum interference in MMI couplers and two-particle quantum walks in coupled waveguides, showing unique quantum behaviour.

We have developed an integrated waveguide approach to photonic quantum circuits for high performance, miniaturization and scalability. We have begun to address the challenges of scaling up quantum circuits using new insights into how controlled operations can be efficiently realised, and demonstrated Shor's algorithm with consecutive CNOT gates and the iterative phase estimation algorithm. We have shown how quantum circuits can be reconfigured, using thermo-optic phase shifters to realise a highly reconfigurable quantum circuit able to perform almost any function on two photonic qubits, and electro-optic phase shifters in lithium niobate to rapidly manipulate the path and polarisation of telecomm wavelength single photons. We have addressed miniaturisation using multimode interference coupler architectures to directly implement NxN Hadamard operations and the `Boson sampling problem', and by using high refractive index contrast materials such as SiOxNy, in which we have implemented quantum walks of correlated photons, and Si, in which we have demonstrated generation of orbital angular momentum states of light. We have incorporated microfluidic channels for the delivery of samples to measure the concentration of a blood protein with entangled states of light. We have begun to address the integration of superconducting single photon detectors and diamond and non-linear single photon sources. Finally, we give an overview of recent work on fundamental aspects of quantum measurement, including a quantum version of Wheeler's delayed choice experiment.