Abstract Quantum information processors exploit the quantum features of superposition and entanglement for applications not possible in classical devices, offering the potential for significant improvements in the communication and processing of information. Experimental realization of large-scale quantum information processors remains a long-term vision, as the required nearly pure quantum behaviour is observed only in exotic hardware such as individual laser-cooled atoms and isolated photons. But recent theoretical and experimental advances suggest that cold atoms and individual photons may lead the way towards bigger and better quantum information processors, effectively building mesoscopic versions of 'Schrödinger's cat' from the bottom up.
Abstract Quantum information processors exploit the quantum features of superposition and entanglement for applications not possible in classical devices, offering the potential for significant improvements in the communication and processing of information. Experimental realization of large-scale quantum information processors remains a long-term vision, as the required nearly pure quantum behaviour is observed only in exotic hardware such as individual laser-cooled atoms and isolated photons. But recent theoretical and experimental advances suggest that cold atoms and individual photons may lead the way towards bigger and better quantum information processors, effectively building mesoscopic versions of 'Schrödinger's cat' from the bottom up.
Quantum information science and atom optics are among the most active fields in modern physics. One of our main activities is to use atomic qubits as quantum memory and exploit photonic qubits for information transfer and processing to achieve efficient linear optics quantum information processing (QIP). On the one hand, utilizing the interaction between laser pulses and ultra-cold atomic ensembles we experimentally investigate the potentials of atomic ensembles in the gas phase to build quantum repeaters for long-distance quantum communication, that is, to develop a new technological solution for quantum repeaters making use of the effective qubit-type entanglement of two cold atomic ensembles by a projective measurement of individual photons by spontaneous Raman processes. On the other hand, building on our long experience in research on multi-photon entanglement, The techniques that are being developed will lay the basis for future large-scale realizations of linear optical QIP with atoms and photons.
Quantum information science and atom optics are among the most active fields in modem physics. In recent years, many theoretical efforts have been made to combine these two fields. Recent experimental progresses [1-3] have shown the in-principle possibility to perform scalable quantum information processing (QIP) with linear optics and atomic ensembles [4]. One of our main activities is to use atomic qubits as quantum memory and exploit photonic qubits for information transfer and processing to achieve efficient linear optics QIP. On the one hand, utilizing the interaction between laser pulses and atomic ensembles we experimentally investigate the potentials of atomic ensembles in the gas phase to build quantum repeaters for longdistance quantum communication [5], that is, to develop a new technological solution for quantum repeaters making use of the effective qubit-type entanglement of two cold atomic ensembles by a projective measurement of individual photons by spontaneous Raman processes. On the other hand, building on our long experience in research on multi-photon entanglement, we are also working on a number of experiments in the field of QIP with particular emphasis on fault-tolerant quantum computation [6], photon-loss-tolerant quantum computation [7] and cluster-state based quantum simulation [8]. In future, by combining the techniques developed in the above quantum memory and multi-photon interference experiments, we will experimentally investigate the possibility to achieve quantum teleportation between photonic and atomic qubits, quantum teleportation between remote atomic qubits and efficient entanglement generation via classical feed-forward. The techniques that are being developed will lay the basis for future large-scale realizations of linear optical QIP with atoms and photons.
Quantum information science and atom optics are among the most active fields in modern physics. In recent years, many theoretical efforts have been made to combine these two fields. Recent experimental progresses have shown the in-principle possibility to perform scalable quantum information processing (QIP) with linear optics and atomic ensembles. One of our main activities is to use atomic qubits as quantum memory and exploit photonic qubits for information transfer and processing to achieve efficient linear optics QIP. On the one hand, utilizing the interaction between laser pulses and ultra-cold atomic ensembles we experimentally investigate the potentials of atomic ensembles in the gas phase to build quantum repeaters for long-distance quantum communication, that is, to develop a new technological solution for quantum repeaters making use of the effective qubit-type entanglement of two cold atomic ensembles by a projective measurement of individual photons by spontaneous Raman processes.
At the most microscopic level, all physical systems are governed by the laws of quantum mechanics. Quantum information processing is the study of how information is gathered, transformed, and transmitted at the quantum level—in atoms, ions, photons, elementary particles, and microscopic solid-state systems, which obey fundamentally quantum mechanical laws. Quantum computers, quantum communication channels, and quantum sensors are devices that can attain the ultimate limits of information processing. The laws of quantum mechanics give rise to counterintuitive effects. Quantum information processors use “quantum weirdness” to perform tasks that classical information processors cannot. Quantum computers are conceived to process information stored on atomic, optical, and solid-state systems: they aim to use counterintuitive effects including quantum superposition and entanglement to perform tasks such as quantum simulation, quantum search, and factoring/code-breaking to solve problems that are hard or impossible on conventional classical computers. Quantum communication systems transmit information encoded in individual photons: they exploit the fact that quantum measurement is inevitably stochastic and destructive to enact quantum-encrypted communication whose security is guaranteed by the laws of physics. Quantum sensors and measurement devices operate at the greatest possible sensitivity and precision allowed by physical law: from magnetometers to quantum clocks to advanced gravitational interferometers (e.g., LIGO), quantum metrology supplies the techniques required to push measurement to its ultimate limits.
Quantum information processing opens up completely new possibilities in communication and computation, that would be impossible in the realms of classical physics. While the benefits of quantum information processing are well understood in theory, it remains a formidable challenge to experimentally implement even simple quantum information processing tasks. Numerous physical architectures have been proposed for preparing and coherently manipulating quantum information. Amongst these, quantum optics has been identified as a particularly promising candidate. In particular this arises from the long decoherence times of single photon states, which can be used to encode logical qubits in a variety of ways. Nonetheless, there remain formidable challenges to implementing large scale quantum information processing using optical qubits. Most notably these include: the preparation of pure indistinguishable photons; efficient number-resolving photo-detection; mode-matching; photon loss; and the non-determinism of entangling gates. Any future large scale implementation of optical quantum information processing protocols will require significant advances on most, if not all these fronts. In this thesis we aim to present a comprehensive overview of the major requirements for optical quantum information processing, understand the effects they have, and how they can be modeled. From this we aim to understand what the realistic technological requirements are to achieve scalable optical quantum information processing, and, where possible, suggest means by which to help achieve these goals.
An extensively pursued current direction of research in physics aims at the development of practical technologies that exploit the effects of quantum mechanics. As part of this ongoing effort, devices for quantum information processing, secure communication, and high-precision sensing are being implemented with diverse systems, ranging from photons, atoms, and spins to mesoscopic superconducting and nanomechanical structures. Their physical properties make some of these systems better suited than others for specific tasks; thus, photons are well suited for transmitting quantum information, weakly interacting spins can serve as long-lived quantum memories, and superconducting elements can rapidly process information encoded in their quantum states. A central goal of the envisaged quantum technologies is to develop devices that can simultaneously perform several of these tasks, namely, reliably store, process, and transmit quantum information. Hybrid quantum systems composed of different physical components with complementary functionalities may provide precisely such multitasking capabilities. This article reviews some of the driving theoretical ideas and first experimental realizations of hybrid quantum systems and the opportunities and challenges they present and offers a glance at the near- and long-term perspectives of this fascinating and rapidly expanding field.