arXiv subjects

Paul Kwiat

Publications and source records attributed to Paul Kwiat.

12 recordsLinked to original sources

arXiv2024

CubeSat single-photon detector module for investigating in-orbit laser annealing to heal radiation damage

Single-photon avalanche photodiodes (SPADs) based on silicon are widely considered for quantum satellite communications but suffer from an increasing dark count rate (DCR) due to displacement damage in their active areas induced by proton radiation. When the DCR of SPADs exceeds a certain threshold, they become unusable for quantum communication protocols. Previous laboratory experiments have demonstrated that laser annealing of SPADs' active area with about 1~W optical power can significantly reduce radiation-induced DCR of synthetically irradiated SPADs. To assess the feasibility of in-orbit laser annealing on constantly irradiated SPADs in low-Earth orbit, we developed a module with a CubeSat form factor capable of both laser and thermal annealing of four silicon SPADs. Here we report the design and ground testing of this module, investigating laser annealing in a simulated space environment. Our results pave the way for an in-orbit trial that may prove this technology useful for future satellite missions with quantum receivers on board.

physics.ins-det↗

arXiv2023

Accelerating Progress Towards Practical Quantum Advantage: The Quantum Technology Demonstration Project Roadmap

Quantum information science and technology (QIST) is a critical and emerging technology with the potential for enormous world impact and is currently invested in by over 40 nations. To bring these large-scale investments to fruition and bridge the lower technology readiness levels (TRLs) of fundamental research at universities to the high TRLs necessary to realize the promise of practical quantum advantage accessible to industry and the public, we present a roadmap for Quantum Technology Demonstration Projects (QTDPs). Such QTDPs, focused on intermediate TRLs, are large-scale public-private partnerships with a high probability of translation from laboratory to practice. They create technology demonstrating a clear 'quantum advantage' for science breakthroughs that are user-motivated and will provide access to a broad and diverse community of scientific users. Successful implementation of a program of QTDPs will have large positive economic impacts.

quant-ph↗

arXiv2022

Coordinated Science Laboratory 70th Anniversary Symposium: The Future of Computing

In 2021, the Coordinated Science Laboratory CSL, an Interdisciplinary Research Unit at the University of Illinois Urbana-Champaign, hosted the Future of Computing Symposium to celebrate its 70th anniversary. CSL's research covers the full computing stack, computing's impact on society and the resulting need for social responsibility. In this white paper, we summarize the major technological points, insights, and directions that speakers brought forward during the Future of Computing Symposium. Participants discussed topics related to new computing paradigms, technologies, algorithms, behaviors, and research challenges to be expected in the future. The symposium focused on new computing paradigms that are going beyond traditional computing and the research needed to support their realization. These needs included stressing security and privacy, the end to end human cyber physical systems and with them the analysis of the end to end artificial intelligence needs. Furthermore, advances that enable immersive environments for users, the boundaries between humans and machines will blur and become seamless. Particular integration challenges were made clear in the final discussion on the integration of autonomous driving, robo taxis, pedestrians, and future cities. Innovative approaches were outlined to motivate the next generation of researchers to work on these challenges. The discussion brought out the importance of considering not just individual research areas, but innovations at the intersections between computing research efforts and relevant application domains, such as health care, transportation, energy systems, and manufacturing.

cs.CY↗

arXiv2022

Quantum Clock Synchronization for Future NASA Deep Space Quantum Links and Fundamental Science

The ability to measure, hold and distribute time with high precision and accuracy is a foundational capability for scientific exploration. Beyond fundamental science, time synchronization is an indispensable feature of public and private communication, navigation and ranging, and distributed sensing, amongst others technological applications. We propose the implementation of a quantum network of satellite- and ground-based clocks with the ability to implement Quantum Clock Synchronization to picosecond accuracy. Implementation of the proposed QCS network offers a double advantage: (1) a more accurate, robust, and secure time synchronization network for classical applications than currently possible, and (2) a resource to fulfill the much more stringent synchronization requirements of future quantum communication networks.

quant-ph↗

arXiv2021

The Deep Space Quantum Link: Prospective Fundamental Physics Experiments using Long-Baseline Quantum Optics

The National Aeronautics and Space Administration's Deep Space Quantum Link mission concept enables a unique set of science experiments by establishing robust quantum optical links across extremely long baselines. Potential mission configurations include establishing a quantum link between the Lunar Gateway moon-orbiting space station and nodes on or near the Earth. In this publication, we summarize the principal experimental goals of the Deep Space Quantum Link mission. These include long-range teleportation, tests of gravitational coupling to quantum states, and advanced tests of quantum nonlocality.

quant-ph↗

arXiv2019

Direct Excitation of a Single Quantum Dot with Cavity-SPDC Photons

The ability to generate mode-engineered single photons to interface with disparate quantum systems is of importance for building a quantum network. Here we report on the generation of a pulsed, heralded single photon source with a sub-GHz spectral bandwidth that couples to indium arsenide quantum dots centered at 942 nm. The source is built with a type-II PPKTP down-conversion crystal embedded in a semi-confocal optical cavity and pumped with a 76 MHz repetition rate pulsed laser to emit collinear, polarization-correlated photon pairs resonant with a single quantum dot. In order to demonstrate direct coupling, we use the mode-engineered cavity-SPDC single-photon source to resonantly excite an isolated single quantum dot.

quant-ph↗

arXiv2010

Optimizing type-I polarization-entangled photons

Optical quantum information processing needs ultra-bright sources of entangled photons, especially from synchronizable femtosecond lasers and low-cost cw-diode lasers. Decoherence due to timing information and spatial mode-dependent phase has traditionally limited the brightness of such sources. We report on a variety of methods to optimize type-I polarization-entangled sources - the combined use of different compensation techniques to engineer high-fidelity pulsed and cw-diode laser-pumped sources, as well as the first production of polarization-entanglement directly from the highly nonlinear biaxial crystal BiB3O6 (BiBO). Using spatial compensation, we show more than a 400-fold improvement in the phase flatness, which otherwise limits efficient collection of entangled photons from BiBO, and report the highest fidelity to date (99%) of any ultrafast polarization-entanglement source. Our numerical code, available on our website, can design optimal compensation crystals and simulate entanglement from a variety of type-I phasematched nonlinear crystals.

quant-ph↗

arXiv2006

Counterfactual computation revisited

Mitchison and Jozsa recently suggested that the "chained-Zeno" counterfactual computation protocol recently proposed by Hosten et al. is counterfactual for only one output of the computer. This claim was based on the existing abstract algebraic definition of counterfactual computation, and indeed according to this definition, their argument is correct. However, a more general definition (physically adequate) for counterfactual computation is implicitly assumed by Hosten et. al. Here we explain in detail why the protocol is counterfactual and how the "history tracking" method of the existing description inadequately represents the physics underlying the protocol. Consequently, we propose a modified definition of counterfactual computation. Finally, we comment on one of the most interesting aspects of the error-correcting protocol.

quant-ph↗

arXiv2005

Precise Creation, Characterization, and Manipulation of Single Optical Qubits

We present the theoretical basis for and experimental verification of arbitrary single-qubit state generation, using the polarization of photons generated via spontaneous parametric downconversion. Our precision measurement and state reconstruction system has the capability to distinguish over 3 million states, all of which can be reproducibly generated using our state creation apparatus. In order to complete the triumvirate of single qubit control, there must be a way to not only manipulate single qubits after creation and before measurement, but a way to characterize the manipulations \emph{themselves}. We present a general representation of arbitrary processes, and experimental techniques for generating a variety of single qubit manipulations, including unitary, decohering, and (partially) polarizing operations.

quant-ph↗

arXiv2003

Taming Entanglement

Using a spontaneous parametric-downconversion source of photon pairs, we are working towards the creation of arbitrary 2-qubit quantum states with high fidelity. Currently, all physically allowable combinations of polarization entanglement and mixture can be produced, including maximally-entangled mixed states. The states are experimentally measured and refined via computer-automated quantum-state tomography, and this system has also been used to perform single-qubit and ancilla-assisted quantum process tomography.

quant-ph↗

arXiv2002

Atomic vapor-based high efficiency optical detectors with photon number resolution

We propose a novel approach to the important fundamental problem of detecting weak optical fields at the few photon level. The ability to detect with high efficiency (>99%), and to distinguish the number of photons in a given time interval is a very challenging technical problem with enormous potential pay-offs in quantum communications and information processing. Our proposal diverges from standard solid-state photo-detector technology by employing an atomic vapor as the active medium, prepared in a specific quantum state using laser radiation. The absorption of a photon will be aided by a dressing laser, and the presence or absence of an excited atom will be detected using the ``cycling transition'' approach perfected for ion traps. By first incorporating an appropriate upconversion scheme, our method can be applied to a wide variety of optical wavelengths.

quant-ph↗

arXiv1999

Two-photon Franson-type experiments and local realism

The two-photon interferometric experiment proposed by Franson [Phys. Rev. Lett. 62, 2205 (1989)] is often treated as a "Bell test of local realism". However, it has been suggested that this is incorrect due to the 50% postselection performed even in the ideal gedanken version of the experiment. Here we present a simple local hidden variable model of the experiment that successfully explains the results obtained in usual realizations of the experiment, even with perfect detectors. Furthermore, we also show that there is no such model if the switching of the local phase settings is done at a rate determined by the internal geometry of the interferometers.

quant-ph↗