Atom chips provide a versatile quantum laboratory for experiments with ultracold atomic gases. They have been used in diverse experiments involving low-dimensional quantum gases, cavity quantum electrodynamics, atom-surface interactions, and chip-based atomic clocks and interferometers. However, a severe limitation of atom chips is that techniques to control atomic interactions and to generate entanglement have not been experimentally available so far. Such techniques enable chip-based studies of entangled many-body systems and are a key prerequisite for atom chip applications in quantum simulations, quantum information processing and quantum metrology. Here we report the experimental generation of multi-particle entanglement on an atom chip by controlling elastic collisional interactions with a state-dependent potential. We use this technique to generate spin-squeezed states of a two-component Bose-Einstein condensate; such states are a useful resource for quantum metrology. The observed reduction in spin noise of -3.7 +/- 0.4 dB, combined with the spin coherence, implies four-partite entanglement between the condensate atoms; this could be used to improve an interferometric measurement by -2.5 +/- 0.6 dB over the standard quantum limit. Our data show good agreement with a dynamical multi-mode simulation and allow us to reconstruct the Wigner function of the spin-squeezed condensate. The techniques reported here could be directly applied to chip-based atomic clocks, currently under development.

Within the last two decades, quantum technologies (QT) have made tremendous progress, moving from Nobel Prize award-winning experiments on quantum physics (1997: Chu, Cohen-Tanoudji, Phillips; 2001: Cornell, Ketterle, Wieman; 2005: Hall, Hänsch-, Glauber; 2012: Haroche, Wineland) into a cross-disciplinary field of applied research. Technologies are being developed now that explicitly address individual quantum states and make use of the 'strange' quantum properties, such as superposition and entanglement. The field comprises four domains: quantum communication, where individual or entangled photons are used to transmit data in a provably secure way; quantum simulation, where well-controlled quantum systems are used to reproduce the behaviour of other, less accessible quantum systems; quantum computation, which employs quantum effects to dramatically speed up certain calculations, such as number factoring; and quantum sensing and metrology, where the high sensitivity of coherent quantum systems to external perturbations is exploited to enhance the performance of measurements of physical quantities. In Europe, the QT community has profited from several EC funded coordination projects, which, among other things, have coordinated the creation of a 150-page QT Roadmap (http://qurope.eu/h2020/qtflagship/roadmap2016). This article presents an updated summary of this roadmap.

Entanglement-based technologies, such as quantum information processing, quantum simulations, and quantum-enhanced metrology, have the potential to revolutionise our way of computing and measuring and help clarifying the puzzling concept of entanglement itself. Ultracold atoms on atom chips are attractive for their implementation, as they provide control over quantum systems in compact, robust, and scalable setups. An important tool in this system is a potential depending on the internal atomic state. Coherent dynamics in this potential combined with collisional interactions allows entanglement generation both for individual atoms and ensembles. Here, we demonstrate coherent manipulation of Bose-condensed atoms in such a potential, generated in a novel way with microwave near-fields on an atom chip. We reversibly entangle atomic internal and motional states, realizing a trapped-atom interferometer with internal-state labelling. Our system provides control over collisions in mesoscopic condensates, paving the way for on-chip generation of many-particle entanglement and quantum-enhanced metrology with spin-squeezed states.

We use a small Bose-Einstein condensate on an atom chip as an interferometric scanning probe to map out a microwave field near the chip surface with a few micrometers resolution. With the use of entanglement between the atoms, our interferometer overcomes the standard quantum limit of interferometry by 4 dB and maintains enhanced performance for interrogation times up to 10 ms. This corresponds to a microwave magnetic field sensitivity of 77 pT/√Hz in a probe volume of 20 μm(3). Quantum metrology with entangled atoms is useful in measurements with high spatial resolution, since the atom number in the probe volume is limited by collisional loss. High-resolution measurements of microwave near fields, as demonstrated here, are important for the development of integrated microwave circuits for quantum information processing and applications in communication technology.

We report a technique that uses clouds of ultracold atoms as sensitive, tunable, and noninvasive probes for microwave field imaging with micrometer spatial resolution. The microwave magnetic field components drive Rabi oscillations on atomic hyperfine transitions whose frequency can be tuned with a static magnetic field. Readout is accomplished using state-selective absorption imaging. Quantitative data extraction is simple and it is possible to reconstruct the distribution of microwave magnetic field amplitudes and phases. While we demonstrate two-dimensional imaging, an extension to three-dimensional imaging is straightforward. We use the method to determine the microwave near-field distribution around a coplanar waveguide integrated on an atom chip. © 2010 American Institute of Physics. ͓doi:10.1063/1.3470591͔ Today, monolithic microwave integrated circuits ͑MMICs͒ are of great importance in science and technology. In particular, they constitute key building blocks of today's communication technology. 1 MMICs also serve as main components of superconducting quantum processors. 2 In our group, a simple MMIC structure has recently been used as a tool for quantum coherent manipulation of ultracold atoms on an atom chip. 3 Function and failure analysis is of crucial importance for the design of MMICs as well as for simulation verification. 4 External port measurements ͑e.g., using a network analyzer͒ offer only limited insight. The microwave ͑mw͒ near-field distribution on the device gives much more information, enabling specific improvement. Therefore, different methods have been developed to measure the spatial distribution of mw near-fields. 5 These methods use diverse physical effects to measure the mw electric or magnetic field. They have in common that they scan the field distribution point-by-point.Here we propose and experimentally demonstrate a highly parallel method that allows for non-invasive and complete ͑amplitudes and phases͒ imaging of the mw magnetic field distribution using clouds of ultracold atoms. 6 In this method, the mw magnetic field drives resonant Rabi oscillations 7 between two atomic hyperfine levels that can be detected using state-selective absorption imaging. 8 The method offers micrometer spatial resolution and a mw magnetic field sensitivity in the 10 −8 T range at frequencies of a few gigahertz. It is a frequency-domain, single-shot technique to measure a two-dimensional field distribution. The method can be extended to measure three-dimensional ͑3D͒ distributions slice by slice. Data extraction is simple, it offers a high dynamic range, and it is intrinsically calibrated since only well-known atomic properties enter in the analysis.For the proof-of-principle experiment presented here, we use our atom chip setup, 3 see Fig. 1. The chip has integrated mw coplanar waveguide ͑CPW͒ structures that were designed for quantum manipulation of ultracold atoms. 3 To demonstrate our method, we analyze the mw magnetic field near this structure. In general, the device to be tested does ...

As the first applications leap out of research laboratories toward commercialization, the global race for dominance in the maturing field of quantum technologies is becoming ever fiercer. To retain its historical lead and kick-start a continent-wide quantum-driven industry and accelerate market take-up, Europe has launched the Quantum Flagship, an ambitious €1 billion, 10 year endeavor. This article provides an overview of the underlying considerations and the current state of the initiative. Furthermore, it briefly presents the 20 projects selected to be at the core of the ramp-up phase of the initiative, which will address core applications of quantum technologies such as communications, computing, simulation, as well as sensing and metrology, all of which are supported by basic science. Finally, we present the broader ecosystem of European funding instruments and institutions which aim to create the next generation of disruptive technologies within quantum sciences, placing Europe as a worldwide knowledge-based industrial and technological leader in this innovative field.

Quantum technologies, such as quantum communication, computation, simulation as well as sensors and metrology, address and manipulate individual quantum states and make use of superposition and entanglement. Both companies and governments have realised the high disruptive potential of this technology. Consequently, the European Commission has announced an ambitious flagship programme to start in 2018. Here, we sum up the history leading to the quantum technologies flagship programme and outline its envisioned goals and structure. We also give an overview of the strategic research agenda for quantum communication, which the flagship will pursue during its 10-year runtime. Why a flagship and why now?We are currently experiencing a 'second quantum revolution'. In the first quantum revolution, the fundamental laws of the microscopic realm were discovered and quantum science was formulated. In the following years, ground-breaking technologies such as the transistor and the laser were developed. These inventions can only be understood and developed with the help of quantum mechanics (e.g. to understand the band structure of a semiconductor or the nature of a coherent state), but they are based on bulk effects, where many quantum degrees of freedom are manipulated at once.In the second quantum revolution, which is unfolding now, technologies are being developed that explicitly address individual quantum states and make use of the 'strange' quantum properties, such as superposition and entanglement, commonly referred to as quantum technologies (QT). Why do we believe that this revolution is happening now? On the one hand, a number of start-up companies were founded over the last decade which offer QT to very specialised markets. Quantum cryptography is among the most advanced QT with highly specialised small and medium-sized enterprises 4 already selling their products to governments, banks and other customers with highest security requirements. On the other hand, and even more importantly, large global companies, including Google [1], IBM 5 , Intel [2], Microsoft [3] and Toshiba 6 have recently started to invest heavily in QT. They are attracting top talents that just a couple of years ago would have only had the choice between pursuing an academic career and leaving the field altogether. Governments are also picking up on the trend and starting large funding programmes in the field 7 . Besides quantum computation, quantum communication is particularly high on the agenda of many countries, especially in China, who plans to invest massively, at a scale larger than the European flagship, and has recently launched a satellite with quantum communication devices [4].

We outline a method to slow paramagnetic atoms or molecules using pulsed magnetic fields. We also discuss the possibility of producing trapped particles by adiabatic deceleration of a magnetic trap. We present numerical simulation results for the slowing and trapping of molecular oxygen.