Less than ten years ago it was realized that quantum theory permits the existence of processes which do not have a defined causal order. To date, several experiments have confirmed the existence of one such process, called the quantum SWITCH, in which it is impossible to say which of two parties acts first. This has since spawned a new field of research on quantum processes with an indefinite causal order. Building on a mathematical analogy to entanglement certification, various methods to quantify the lack of a causal order have been proposed and demonstrated. These characterization techniques range from playing specially designed games to the measurement of a so-called causal witness. Despite these promising strategies, there has not yet been a complete characterization of the quantum SWITCH and no measurement of its process fidelity. Here we present a new protocol to perform causal tomography which we carry out using a novel implementation of the quantum SWITCH, based on time-bin qubits in optical fiber. Our new implementation is readily scalable to more than two parties and, hence, could be used to observe the scaling advantages of certain quantum games. Using this platform, we perform the first measurement of the process fidelity of the quantum SWITCH.

“Kicking” a quantum system by subjecting it to a pulsed time-dependent Hamiltonian can give rise to a rich array of behaviors, from localization to multifractality. In this talk we will describe two recent experiments on kicked quantum matter using ultracold neutral atoms. In the first experiment, we measured the “quantum boomerang effect,” a fundamental dynamical feature of Anderson-localized matter which was only recently theoretically predicted and has not to our knowledge been observed before. The second experiment explores an extended multifractal phase in a kicked quasicrystal, using a technique of “apodized” Floquet engineering. The results illuminate a variety of phenomena ranging from the interplay of ergodicity and localization to new techniques of quantum control.

A deeper understanding of the physical processes behind the emergence of photoelectron current pulse (PCP) statistics could help relaxing the source requirements for quantum computers, in choosing nonlinear vs. linear processing of light. Einstein’s photoelectric equation is an energy-balancing “bullet model”. The “bullet-model” over-rides both the classical and the quantum Superposition Principle (SP). SP requires first summing the joint amplitude stimulation experienced by the detecting dipoles by all the incident complex amplitudes, followed by the square modulus operation executed by the detecting dipoles to absorb the quantum-cupful of energy. We have been accommodating this “bullet model” via the prevailing belief that wave-particle duality is our new “confirmed knowledge”, instead of acknowledging our ignorance about the true nature of light. We will use the semiclassical model of photons as time-finite random light pulses stimulating a detecting molecule to its excited state of Ѱ. The molecule then absorbs the quantum of energy through the execution of the square modulus operation, Ѱ*Ѱ, and release the quantum mechanically bound electron. The lifetime of releasing the bound electron is very short as they are in quantum bands, rather than in sharp quantum levels. Each one of the released electron is then amplified, through complex electronic processes, by a factor of as much as 109, to generate one easily measurable photoelectric current pulse, or PCP’s. Therefore, the emergence of the PCP statistics is a combined function of (i) fluctuations in the incident light, (ii) fluctuations in the electron emission moments and (iii) noise introduced during the amplification process. In this paper, we will consider a classical linear approach in smoothing the average energy delivery on to a photodetector using the natural pulse replication property of a Fabry-Perot interferometer (FPI) and hence narrow the PCP statistical spread. If our model is correct, we should be able to derive the PCP-statistics for different sources using the fundamental amplitude and phase characteristics of various real sources. We have also proposed specific experiments to validate our model.

Quantum technology and its application in quantum computing has been gaining relevance and making incredible strides in the achievement of practical implementations of this new form of hardware acceleration. However, in order to really succeed as a computational choice in the many application fields — from science to economy—, the devices need to be programmable and within reach to non-quantum users. There are multiple approaches to solve the quantum computing riddle. This paper looks at two of them, Boson sampling and qubit gate-based quantum accelerators, and compares their implementation and programmability of a common problem: the maximum clique problem.

Over the last decades, the combination of quantum computing and machine learning has opened many possibilities, for example enhancing machine learning algorithms through quantum platforms. However, one of the current challenges consists in combining the linear unitary evolution of closed quantum systems with the nonlinearity required by neural networks, which are currently the most widely used and versatile machine learning algorithms. This issue can now be addressed by a novel photonic tool, the quantum memristor,1 which displays a nonlinear behavior, while preserving quantum coherence, through a weak controlled interaction of its input state with the environment. Here, we show how its operation can be extended to deal with higher frequency modulations of the input and, possibly, with a simplification in its scheme. This method can prove useful for the future implementation of memristor-based quantum neural networks.

The next generation of quantum computers will be scaled up from those which currently incorporate a few dozen qubits, to those of a few hundred with the development of noisy intermediate-scale quantum (NISQ) devices. This greatly increases the decoherence rate of any operation performed using NISQ hardware even under cryogenic conditions. Recently, much effort has been put into researching plasmonic-based devices that are able to perform ultrafast (picosecond) logic operations on a time scale that is faster than the decoherence rate of the system, while being able to operate nearer to room temperature. Plasmonic-based structures that use quantum dots as qubits are considered viable sources for room temperature quantum networks given their relatively low decoherence rate and their overall ease to fabricate compared to the often-used superconducting, i.e., SQUID-based devices. For quantum computing, one requires a reliable source of entangled particles which are compatible with repeaters and quantum error correction. Herein, we investigate the possibilities of time-dependent multipartite entanglement using a plasmonic-based archetype which couples quantum dots to a surface plasmon mode of a near-field transducer (NFT) and is fully integrated with a photonic waveguide. We demonstrate excellent fidelities of entanglement (>0.99) while varying the dipole moment and further investigate the effect of manipulating between the weak to strongly driven regimes. Altogether, we present a novel concept suitable for the implementation of dynamic quantum logic gates on an ultrafast scale closer to room temperature.

We analyse the behaviour of single photon states within rectangular waveguides. The fields were solved for using normal modes of rectangular waveguides. The system is taken to be coupled to a cavity-atom system and the coupling between the cavity and waveguide was analysed to compute a coupling frequency. The single mode approximation was used assuming a Jaynes-Cummings form for the Hamiltonian to arrive at field operator expressions. These were used along with photodetection theory to compute the output detection probabilities for single photon states in the dominant mode. Finally, the single photon state was analysed within an MZI and a directional coupler. Y splitters and combiners were assumed to have 50% power division. Our results suggest that for single photon states, there is little to no deviation from the classical case in terms of input and output.

In this general brief overview, we discuss the different types of nodes and associated levels of security that can be considered in a quantum key distribution (QKD) network. This classification lead to different possible scenarios for QKD repeater chains and, more generally, for QKD network architectures.

We extend the asymptotic security of continuous variable quantum key distribution using one-way and two-way quantum communication to a multi-way setting: Quantum signals travel many times between the parties before the final detection. We assume that the encoded signals are Gaussian-modulated coherent states that travel each time through the same Gaussian channel characterized by loss and thermal noise. We then quantify the reverse-reconciliation performance of the protocol presenting results for even or odd numbers of signal exchange.

The Air Force Institute of Technology (AFIT) is building a quantum optics and quantum information laboratory to study single photon phenomena and its applications. We propose an experiment to characterize the effects of atmospheric turbulence on single photons and entangled pair of photons as a function of statistical quantities that define a turbulent atmosphere (such as the Fried parameter, Greenwood frequency, Rytov variance, ect).This presentation details the initial experiment studying single photon propagation using an atmospheric turbulence simulator that statistically represents ground-to-space quantum communications.

Quantum walks (QWs) have emerged from fundamental research to be one of key processes in quantum information technology including quantum computing and quantum communication. In this paper, we present results of our numerical investigation of quantum walks (QWs) in different types of 2D arrays of waveguides. We show (i) the localized QWs in quasiperiodic arrays based on Fibonacci sequences are highly controllable due to the deterministically disordered nature of quasiperiodic photonic lattices, (ii) 2D arrays of waveguides can also be used as platforms to realize important effects for special applications such as exponential speedup in quantum search and quantum topology photonics and finally, (iii) results of multiple photons QWs in 2D programable directional couplers can be useful for designing quantum photonics gates.

Quantum technologies are also relying strongly on semiconductors and especially optical semiconductor technologies based on III-V compound semiconductors. Quantum technology can leverage from various semiconductor laser solutions. Laser diodes and related technologies can be used for excitation for quantum systems and quantum control of molecules. Examples of such quantum systems are single photon emitters, timing sources used for picosecond pulses, and frequency combs. In this talk, we will discuss the key semiconductor manufacturing technologies for quantum optics and opportunities and challenges in integration of these technologies and products into quantum systems with over 20 years’ experience in designing and manufacturing III-V optical semiconductors.

We investigate cavity-assisted Stimulated Raman Adiabatic passage (STIRAP) schemes in semiconductor quantum dots (QDs) embedded in an optical cavity as a route for generation of high-quality single photons with programmable waveform. This work addresses the need for high-purity, indistinguishable photons in linear quantum computing, boson sampling, and quantum communications. We develop a time-dependent Maxwell-pseudospin model of single-photon generation through cavity-assisted adiabatic passage in a Λ-system isolated in a neutral InAs QD in a realistic GaAs/AlGaAs micropillar cavity. As a model Λ-system, we consider QD biexciton triplet states coupled to dark-exciton states by a circularly polarised pulse and a cavity field. Our simulations demonstrate control of the emitted single-photon pulse waveform by the driving pulse characteristics: shape, duration, intensity and detuning.

Quantum technology can leverage from various semiconductor laser solutions – depending on the technology, lasers can be used for excitation for quantum systems and quantum control of molecules. Examples of such quantum systems are single photon emitters, timing sources used for picosecond pulses, and frequency combs. Necessary performance parameters for such laser devices are single-mode operation, narrow spectral line width, and frequency stability over operation lifetime. Wavelength and optical output power of the diode laser devices can vary depending on the system. Narrow spectral linewidth with frequency stability can be achieved with distributed Bragg reflector (DBR) or distributed feedback (DFB) lasers with quarter-lambda phase shift is included in the grating, or with external cavities. In addition, efficiency of the systems can be improved when using laser diode arrays instead of single-emitter chips. Further improvement can be introduced by implementing individually addressable laser diode array operation (IAB). In this work, we present ways to improve our state-of-the-art low pitch laser diode array operation, within NIR wavelengths 780 to 930 nm. Emitter pitches as low as 20 μm introduce complex interference and cross-talk phenomena that can appear as multiple transverse modes. These matters can be addressed with device design starting from the epitaxial structures, gratings, ridge waveguide optimizations up to facet coating of the arrays. Such arrays offer opportunities for dense device design and flexibility for end applications in, e.g., external cavity operating applications or silicon photonics.

This PDF file contains the front matter associated with SPIE Proceedings Volume 12243 including the Title Page, Copyright information, and Table of Contents.