**Invited Speakers**

Below is this list of invited speakers for QCMC 2018. Each invited speaker will give a 25 minute talk and will be allowed 5 minutes for questions.

- Barsotti, Lisa (MIT, USA):
**The quantum side of gravitational wave detectors**—*The recent observations of gravitational waves have been enabled by a new generation of LIGO detectors, Advanced LIGO, the most sensitive laser interferometers ever built. The Advanced LIGO detectors are limited by quantum noise across the entire detection band, and can benefit from quantum technology to further extend their astrophysical reach.*

In my talk I will describe the Advanced LIGO detectors and prospects for pushing the quantum limit using squeezed states of light. - Caves, Carl (University of New Mexico):

**Hearne Lecture**- Friday 3/16/18, 2:30 PM

**What the #$*! Do We (K)now!? about Quantum Mechanics**—*There is a world of consummate strangeness at our fingertips, provided our fingers are so exquisitely fine as to be able to feel and manipulate individual atoms and molecules. Ever since the realization that the behavior of atoms and molecules is governed by the laws of quantum mechanics, it has been understood that the world of the very small is nothing like the familiar world of everyday experience. Yet only recently has it been fully appreciated just how different the world of quantum systems is---and how that difference might be exploited to do things that can't be done in our mundane everyday world. I will illustrate how weird the atomic-scale world really is and indicate how we might take advantage of that weirdness using new technologies for manipulating atomic-scale systems. You will have to pay close attention, but the reward will be a glimpse of the truly astonishing nature of the world we all inhabit.* - Croke, Sarah (University of Glasgow, Scotland):
**Quantum measurement in the age of small quantum devices**—*Technology has progressed to the stage where we now have control over small numbers of quantum systems. In addition to searching for a definitive demonstration of computational improvement over classical methods, what can we do with such devices? In this talk I will discuss measurement with small quantum probes: a measurement apparatus that can retain coherence in between interactions gives an explicit means to perform joint measurements on a sequence of external systems. What measurements can we perform with a small quantum device that are impossible without? I will present some simple and perhaps surprising cases in which a quantum probe gives little or no improvement. I will also introduce the simplest such measurement device, an extension of the canonical von Neumann probe, and discuss aspects of measurement with such a device.* - Curty, Marcos (University of Vigo, Spain):
**Towards implementation security of quantum key distribution**—*Quantum key distribution (QKD) holds the promise of offering information-theoretically secure communications based on the laws of quantum physics. In practice, however, it does not because current security proofs of QKD rely on assumptions which are not satisfied by the real systems. This includes, for instance, the assumption that the QKD setups do not contain malicious devices and they are in a protected space devoid of any unwanted information leakage, where the legitimate parties can privately generate, process and store their classical data by means of trusted classical post-processing units. Here, we present recent results that relax these unrealistic and hardly feasible requirements to recover the security of practical QKD.* - Demkowicz-Dobrzański, Rafał (University of Warsaw):
**The Great Unified Theory of Quantum Metrology**—*A general model of unitary parameter estimation in presence of Markovian noise is considered, where the parameter to be estimated is associated with the Hamiltonian part of the dynamics. In absence of noise, unitary parameter can be estimated with precision scaling as 1/T, where T is the total probing time. A simple algebraic condition involving solely the operators appearing in the quantum Master equation, decides whether 1/T or 1/\sqrt{T} scaling of precision is achievable using the most general adaptive quantum estimation strategies.* - Dressel, Justin (Chapman University, USA):
**Watching Superconducting Qubits with Microwaves**—*It has recently become experimentally possible to monitor the energy levels of a superconducting transmon qubit continuously in time using microwave fields. Such measurements weakly perturb the qubit per unit time, lead to a competition between unitary Hamiltonian dynamics and non-unitary collapse dynamics. I review several subtleties about modeling this measurement process, and discuss several recent achievements made in collaboration with the Siddiqi laboratory at UC Berkeley. Achievements include conditioned trajectory statistics, simultaneous measurements of multiple non-commuting observables, and the active use of the quantum Zeno effect with a moving measurement basis for qubit control.* - Englund, Dirk (MIT, USA):
**Large-Scale Programmable Photonic Circuits and Applications in Quantum Information Processing**—*Photonic integrated circuits (PICs) have become increasingly important in classical communications applications over the past decades, including as transmitters and receivers in long-haul, metro and datacenter interconnects. Many of the same attributes that make PICs attractive for these applications — compactness, high bandwidth, and the ability to control large numbers of optical modes with high phase stability — also make them appealing for quantum information processing. The first part of this talk will review our recent progress in adapting one of the leading PIC architectures—silicon photonics—for various quantum secure communications protocols. The second part of the talk will consider how photonic integrated circuits technology can extend the reach of quantum communications through all-optical and memory-based quantum repeater protocols. Beyond quantum communications, PICs are also finding application in quantum computing and in classical signal processing applications, including artificial neural networks.* - Fuentes, Ivette (University of Vienna, Austria):

Given by Richard Howl**Detecting gravitational waves with phonons of a BEC**—*With the observation of gravitational waves (GWs) from the merging of binary black hole and neutron star systems in LIGO and Virgo, we are now entering an era of GW astronomy. Over 400 years ago Galileo first observed the Universe when he pointed his telescope to the sky and saw moons of Jupiter through the the visible region of electromagnetic radiation. Since then we have continued to explore the electromagnetic spectrum from low-frequency radio waves to high-frequency gamma rays, finding new unexpected discoveries such as pulsars and gamma ray bursts. LIGO and Virgo have opened a new window through which we can observe the Universe (Hz-kHz) but, as with electromagnetic radiation, there are many more interesting GW frequencies to explore. This requires the development of new GW detectors. Recently, we have shown that, by employing quantum resonance effects and metrology in a Bose-Einstein condensate (BEC), high frequency GWs could be detected. As well as opening a new window onto the Universe, this detector could be based in experimental labs, facilitating the development of many detectors around the world and, therefore, high-positioning of signals. In this talk, the quantum GW detector is introduced and recent developments such as studies of thermal noise, decoherence and simulations are presented.* - Heurs, Michèle (Max Planck Institute):
**Quantum noise reduction schemes for interferometric gravitational wave detection**—*"The first direct detection of gravitational waves from a binary black hole merger in September 2015 heralded the start of gravitational wave astronomy. Five detections later, the first detection of a merger of two neutron stars has provided multi-messenger astronomy with a new observation method. This is only the start of this exciting new era - for statistically meaningful gravitational wave astronomy it is imperative to continually improve detector sensitivity and hence increase the detection rate.*

The current second generation of interferometric gravitational detectors will be quantum limited over most of their detection band (for Advanced LIGO this will be for all frequencies above 12 Hz [S. Hild, Class. Quant. Grav. 29 (2012)]) as soon as their design sensitivity is reached. At first glance this quantum limit might appear fundamental in nature. However, different approaches exist to increase gravitational wave detector sensitivity beyond the quantum frontier, or even to surpass the standard quantum limit of interferometry (the squareroot of the quadratic sum of quantum shot noise and quantum radiation pressure noise in the interferometer, with the laser power as parameter).

I will talk about the standard quantum limit in interferometric gravitational wave detectors and exemplify methods to surpass it. In particular I will explain the principle behind Coherent Quantum Noise Cancellation [Tsang and Caves, Phys. Rev. Lett 105, 123601 (2010); and Wimmer et al., Phys. Rev. A. 89(5) 053836 (2014)], an all-optical radiation pressure noise cancellation scheme based on destructive interference with an anti-noise process, which is described by the same math as effective negative mass noise cancellation schemes in (hybrid) atomic systems [Møller, Nature 547, 191-195 (2017)]." - Howell, John (Hebrew University of Jerusalem, Israel):
**Compressive Quantum Sensing**—*Compressive sensing utilizes sparsity to realize efficient image reconstruction. It is a valuable processing technique when cost, power, technology or computational overhead are limited or high. In the quantum domain technology usually limits efficient acquisition of weak or fragile signals. I will discuss the basics of information theory, compression, and compressive sensing. I will then discuss our recent work in compressive sensing. The topics of discussion include low-flux laser Radar, photonic phase transitions, high resolution biphoton ghost imaging, Ghost object tracking, 3D object tracking and high dimensional entanglement characterization. I will touch lightly on our current work of rapid wavefunction reconstruction and wavefront sensing. As an example (shown below), we were able efficiently and rapidly reconstruct high dimensional joint probability functions of biphotons in momentum and position. With conventional raster scanning this process would take approximately a year, but using double-pixel compressive sensing, the pictures were acquired in a few hours with modest flux.* - Jennewein, Thomas (University of Waterloo, Canada):
**Observation of genuine three-photon interference**—*Multiparticle quantum interference is critical for our understanding and exploitation of quantum information, and for fundamental tests of quantum mechanics. A remarkable example of multi-partite correlations is exhibited by the Greenberger-Horne-Zeilinger (GHZ) state. In a GHZ state, three particles are correlated while no pairwise correlation is found. In a recent experiment we demonstrated three-photon interference which does not originate from two-photon or single photon interference. We observed a phase-dependent variation of three-photon coincidences with 90.5 \pm 5.0 % visibility in a generalized Franson interferometer using energy-time entangled photon triplets created using cascaded spontaneous parametric down-conversion. The demonstration of these strong correlations in an interferometric setting provides new avenues for multiphoton interferometry, fundamental tests of quantum mechanics and quantum information applications in higher dimensions.* - Jiang, Liang (Yale University, USA):
**Quantum control and error correction with superconducting circuits**—*We have developed an efficient quantum control scheme that allows for arbitrary quantum processes on a cavity mode using strongly dispersive qubit-cavity interaction and time-dependent drives. In addition, we have discovered a new class of bosonic quantum error correcting codes, which can correct both cavity loss and dephasing errors. Our control scheme can readily be implemented using circuit QED systems and extended for quantum error correction to protect information encoded in bosonic codes. Moreover, engineered dissipation can also implement holonomic quantum computation using superconducting circuits.* - Klempt, Carsten (Leibnitz University, Germany):
**EPR and spatial-mode entanglement in spinor Bose-Einstein condensates**—*Spin changing collisions in alkaline Bose-Einstein condensates can be employed to generate highly entangled atomic quantum states. Here, we will report on the generation of two classes of entangled states. Firstly, we demonstrate the generation of two-mode squeezed vacuum states and record their characteristic quadrature correlations by atomic homodyning. We prove that the correlations fulfill Reid’s criterion [1] for continuous-variable Einstein-Podolsky-Rosen entanglement. The homodyne measurements allow for a full tomographic reconstruction, yielding a two-mode squeezed state with a 78% fidelity. The created state can be directly applied to atom interferometry, as is exemplified by an atomic clock measurement beyond the Standard Quantum Limit.*

Secondly, we demonstrate entanglement between two spatially separated atomic modes. The entangled state is obtained by spatially splitting a Twin Fock state of indistinguishable atoms. The method opens a path to exploit the recent success in the creation of many-particle entanglement in ultracold atoms for the field of quantum information, where individually addressable subsystems are required. Finally, we will show how the measurement protocol can be extended to perform a Bell test of quantum nonlocality. [1] M. Reid, Phys. Rev. A 40, 913–923 (1989) - Kok, Pieter (University of Sheffield, UK):
**Optimal Quantum Imaging of Distant Black Bodies**—*The measurement of an object’s spatial configuration is important in many disciplines, from astronomy to engineering. We present the quantum optimal estimator for the spatial configuration of a distant body based on the black body radiation received in the far-field—this can be considered a form of reconstructive imaging. In doing so we must deal with multi-parameter quantum estimation of incompatible observables, a problem that is thus far not very well understood. We compare our optimal observables to the two mode analogue of lensed imaging and find that the latter is far from optimal, even when compared to measurements which are separable. To prove the optimality of the estimators we show that they minimise the cost function weighted by the quantum Fisher information—this is equivalent to maximising the average fidelity between the actual state and the estimated one.* - Lam, Ping Koy (Australia National University, Melbourne):
**Multiparameter Optimisation of a Magneto-Optical Trap Using Deep Learning Artificial Neural Networks**—*Many important physical processes have dynamics that are too complex to completely model analytically. Optimisation of such processes often relies on intuition, trial-and-error, or the construction of empirical models. Machine learning based on artificial neural networks has emerged as an efficient means to develop empirical models of complex systems. We implement a deep learning artificial neural network to optimise the magneto-optic cooling and trapping of neutral Rb atomic ensembles. When the optical density of an atomic ensemble is high, many-body interactions start to give rise to complex dynamics that preclude precise analytic optimisation of the cooling and trapping process. The solution identified by our neural networks produces higher optical densities and is radically different to the smoothly varying adiabatic solutions commonly used. Machine learning may provide a pathway to a new understanding of the dynamics of the cooling and trapping processes in cold atomic ensembles.* - Lett, Paul (NIST, Maryland, USA):
**Two-mode squeezing in interferometry and imaging**—*We have been developing a source of two-mode squeezing based on 4-wave mixing in Rb vapor. Using this source we have demonstrated a truncated version of the SU(1,1) interferometer based on nonlinear interactions. With this device we have demonstrated a 4 dB improvement over the shot-noise limit for phase measurements at low intensities. We have also been developing the source to provide squeezing at very low-frequencies and we have now made several improvements to obtain intensity-difference squeezing below 20 Hz. We hope to use this to enable direct intensity-difference imaging on a ccd camera.* - Ling, Alexander (National University of Singapore):
**Progress in satellite QKD and considerations for the future**—*The first step in a global quantum internet would be the successful transmission of quantum communication signals between continents. This first milestone has been successfully reported by the Micius mission, with a number of other concepts reaching experimental maturity in the coming years. I will provide an overview of the recent progress and discuss how nanosatellites emerging from a New Space paradigm can help accelerate the development of space-capable quantum systems, using our own development experience at the Centre for Quantum Technologies.* - Lu, Chao-Yang (USTC, China):
**Multi-photon quantum boson-sampling machines**—*We develop single-photon sources that simultaneously combines high purity, efficiency, and indistinguishability. We demonstrate entanglement among ten single photons. We construct high-performance multi-photon boson sampling machines to race against classical computers.* - Monroe, Christopher (University of Maryland, US):

Given by Norbert Linke**Quantum algorithms with trapped ions**—*Trapped ions are a promising candidate system to realize a scalable quantum computer. We present a modular quantum computing architecture comprised of a chain of 171Yb+ ions with individual Raman beam addressing and individual readout [1]. We use the transverse modes of motion in the chain to produce entangling gates between any qubit pair. This creates a fully connected system which can be configured to run any sequence of single- and two-qubit gates, making it in effect an arbitrarily programmable quantum computer that does not suffer any swap-gate overhead [2]. Recent results from different quantum algorithms on five ions will be presented, including a quantum error detection protocol that fault-tolerantly encodes a logical qubit [3], and a 3-qubit Grover search where we implemented a complete oracle data base [4]. I will also discuss current work and ideas to scale up this architecture.* - Oberthaler, Markus (University of Heidelberg, Germany):

Given by Helmut Strobel**Genuine multipartite entanglement and Einstein-Podolsky-Rosen steering of atomic clouds**—*To generate a squeezed vacuum state, we use spin mixing in a tightly confined Bose-Einstein condensate of 87Rb in a single spatial mode. We show experimentally that the corresponding particle entanglement can be spatially distributed by self-similar expansion of the atomic cloud in a waveguide potential. Spatially resolved spin read-out is used to reveal Einstein-Podolsky-Rosen (EPR) steering between distinct parts of the expanded cloud. To quantify the connection between the strength of EPR steering and genuine multipartite entanglement we construct a witness, which testifies up to genuine five-partite entanglement.* - O'Brien, Jeremy (University of Bristol, UK):

Given by Jonathan Matthews**Homodyne detection on-chip for large scale silicon quantum photonics**—*Silicon-based quantum photonic devices are rapidly growing in capability and complexity. This offers highly-multi-mode structures that coherently manipulate photonic quantum information with high fidelity. This technology is being used in quantum physics and quantum information experiments, and it is proposed as a means to realize large-scale quantum processors. We report a demonstration of a silicon photonics design comprising 148 components, that we use to implement an arbitrary 2-qubit processor acting on photonic qubits. The ability to characterize such devices and measure quantum states within the photonic chip becomes increasingly important as the complexity of components increase further and as new component designs and capabilities are introduced. To contribute to these needs, we present a first realization of an on-chip homodyne detector with performance characteristics suitable for measurement of quantum states.* - Okamoto, Ryo (Kyoto University):
**Photonic quantum circuits for quantum measurement: a quantum shutter closing two slits simultaneously and adaptive quantum state estimation**—*In this talk, we report two recent progresses on photonic quantum circuits for quantum measurement. First, we show a photonic quantum circuit for demonstrating a quantum shutter which can simultaneously close two slits in a double slit experiment. We overcame the difficulty to realize the quantum shutter by employing photonic quantum routers. The observed reflectance ratio clearly surpasses the classical limit, shedding new light on the unusual physical properties of quantum operations. In the second part, we report the experimental demonstration of adaptive quantum state estimation for unknown photonic qubits. The measurement configuration is updated using the results of each photon detection event. The experimental results demonstrate both strong consistency and asymptotic efficiency through several rigorous statistical tests. Furthermore, we show that the distribution of the states estimated using an adaptive quantum state estimation is significantly different from that obtained by conventional state tomography and agrees well with theoretical predictions.* - Polzik, Eugene (Niels Bohr Institute, Denmark):
**Measurement of motion in a negative mass reference frame: from nanomechanics to gravitational wave detectors**—*A continuous measurement of a position of an object imposes a random quantum back action (QBA) perturbation on its momentum. This randomness translates with time into position uncertainty, thus leading to the well known uncertainty of the measurement of motion. As a consequence, and in accordance with the Heisenberg uncertainty principle, the QBA puts a limitation—the so-called standard quantum limit—on the precision of sensing of position, velocity and force. In this talk I will first present the results of the experiment where motion of a mechanical oscillator is tracked with the precision not restricted by the QBA. This is achieved by measuring the motion in a special reference frame linked to an atomic spin system with an effective negative mass. I will then outline a proposal for employing this principle for reaching beyond the SQL precision with Gravitational Wave Detectors, such as LIGO and the Hannover 10m prototype.* - Regal, Cindy (JILA, Boulder, Colorado, US):

Given by Peter Burns**Harnessing electro-optic correlations to improve an efficient mechanical converter**—*A mechanical link between superconducting circuits and the optical domain is an appealing route to a large-scale quantum network. We show that vibrational noise -- ubiquitously introduced by such a link -- can be overcome by harnessing microwave-optical correlations. We construct a microwave-mechanical-optical converter operating at 100 mK, and demonstrate an unprecedented conversion efficiency of 47%. Discovering that vibrational noise produces correlations between microwave and optical outputs, we implement a classical feedforward protocol that improves the recovery of a weak, upconverted signal and reduces noise by 59%, to 38 photons of added noise, for this high-efficiency device. Our results introduce an intriguing alternative method for handling errors introduced by thermal noise.* - Schnabel, Roman (University of Hamburg, Germany):
**Gaussian Entanglement and Quantum Key Distribution**—*Einstein-Podolsky-Rosen entangled light with Gaussian quantum statistics of a continuous-variable (CV) allows for quantum key distribution (QKD) with one-sided device independent security [1]. Furthermore, since a single measurement that is taken on Alice’s and Bob’s sites can yield many bits, CV QKD is envisioned to provide high data rates. Since CV QKD does not use conditioning on modes that contain photons, however, decoherence does strongly limit the achievable distance. Iterative (multistep) entanglement distillation protocols have long been proposed to overcome decoherence, but their probabilistic nature makes them inefficient since the success probability decays exponentially with the number of steps unless quantum memories are used. This talk reports on our proof-of-principle experiment that demonstrated efficient iterative entanglement distillation without quantum memories [2]. An outlook with regard to useful real-world applications of entanglement-based CV QKD is given.* - Sørensen, Anders (Niels Bohr Institute):

Given by Oleksandr Kyriienko**Floquet quantum simulation**—*In this talk I will discuss the advances in the field of quantum simulation, the available approaches, and present recent results on quantum simulation with the Floquet approach. Searching for optimal algorithms for the modern setups with limited resources, I will show that it can be used as an efficient quantum simulation strategy for superconducting circuits platform. Considering the example of a modern transmon-based sample, this for instance can allow to simulate various spin models using periodically modulated drives. Next, I will discuss its potential application for the observation of discrete time crystals. Finally, the roadmap for studying symmetry protected topological phases with superconducting circuits will be presented.* - Tsang, Mankei (National University of Singapore):
**Seize the Moments: Enhancing Moment Estimation for Subdiffraction Incoherent Imaging**—*I propose a far-field imaging method called spatial-mode demultiplexing (SPADE) to estimate the moments of an arbitrary subdiffraction object. I show that the estimation errors can be lower than the Cramer-Rao bounds for direct imaging by orders of magnitude. Realizable with linear optics and photon counting, SPADE should find applications in both observational astronomy and fluorescence microscopy, such as object size and shape estimation. The quantum optimality of the method remains an open problem.* - Vladen, Vuletić (MIT, USA):
**Manipulating individual quanta: photon molecules and 51 atomic qubits**—*Atomic Rydberg states can be used to implement controllable long-distance interactions between individual quanta. By coherently coupling light to Rydberg excitations in a dense atomic medium, we have realized a highly nonlinear optical medium. In this medium, the interactions between individual photons are so strong that two photons can even form a bound state. I will also discuss the use of Rydberg interactions to realize a many-atom quantum simulator with up to 51 individually trapped atoms. We observe a quantum phase transition between a disordered state and a state with antiferromagnetic order, as well as long-lived oscillations after a sudden quench.* - Waks, Edo (University of Maryland, USA):
**Controlling light with a single spin**—*This talk will describe our recent efforts to create strong interactions between single photons and spins using nanophotonics, and to use them to generate strong photon-photon interactions.* - Ye, Jun (JILA, Boulder, Colorado):

Given by Giacomo Valtolina**Towards low temperature phases of fermionic polar molecules**—*Ultracold polar molecules interact via long-range, anisotropic dipole-dipole potentials, allowing the realization of novel many-body quantum phases. Proposed areas of study for polar molecule lattice systems include spin-orbit coupling, topological phases, and exotic superfluidity. Having recently produced a bulk gas of 100,000 ground state potassium-rubidium molecules on a redesigned apparatus, we present progress towards evaporation of molecules in a one-dimensional optical lattice. To manipulate molecular rotational states and control interactions, the apparatus contains in-vacuum electrodes for generating microwave fields and large (30 kV/cm) homogeneous DC electric fields including adjustable field gradients. Future experiments will explore preparation of low-entropy optical lattice samples and microscopy of dipolar spin Hamiltonians.*