The connection between the quantum-vacuum geometric phases (which originates from the vacuum zero-point electromagnetic fluctuation) and the non-normal product procedure is considered in the present Letter. In order to investigate this physically interesting geometric phases at quantum-vacuum level, we suggest an experimentally feasible scheme to test it by means of a noncoplanarly curved fiber made of gyrotropic media. A remarkable feature of the present experimental realization is that one can easily extract the nonvanishing and nontrivial quantum-vacuum geometric phases of left- and/or right- handed circularly polarized light from the vanishing and trivial total quantum-vacuum geometric phases.
An experimentally feasible realization of testing quantum-vacuum geometric phases of photons by using a gyrotropic-medium optical fibre via Casimir's effect is proposed.
We employed an electrically-driven polarization controller to implement anisotropic depolarizing quantum channels for the polarization state of single photons. The channels were characterized by means of ancilla-assisted quantum process tomography using polarization-entangled photons generated in the process of spontaneous parametric down-conversion. The demonstrated depolarization method offers good repeatability, low cost, and compatibility with fiber-optic setups. It does not perturb the modal structure of single photons, and therefore can be used to verify experimentally protocols for mana…
We compare several optical implementations of phase-covariant cloning machines. The experiments are based on copying of the polarization state of a single photon in bulk optics by special unbalanced beam splitter or by balanced beam splitter accompanied by a state filtering. Also the all-fiber based setup is discussed, where the information is encoded into spatial modes, i.e., the photon can propagate through two optical fibers. Each of the four implementations possesses some advantages and disadvantages that are discussed.
Multi-color entangled states of light including low-loss optical fiber transmission and atomic resonance frequencies are essential resources for future quantum information network. We present the experimental achievement on the three-color entanglement generation at 852 nm, 1550 nm and 1440 nm wavelengths for optical continuous variables. The entanglement generation system consists of two cascaded non-degenerated optical parametric oscillators (NOPOs). The flexible selectivity of nonlinear crystals in the two NOPOs and the tunable property of NOPO provide large freedom for the frequency select…
An optical realization of the tunneling dynamics of two interacting bosons in a double-well potential, based on light transport in a four-core microstructured fiber, is proposed. The optical setting enables to visualize in a purely classical system the entire crossover from Rabi oscillations to correlated pair tunneling and to tunneling of a fragmented pair in the fermionization limit.
In this letter, we report an experimental realization of distributing entangled photon pairs over 100 km of dispersion-shifted fiber. In the experiment, we used a periodically poled lithium niobate waveguide to generate the time-energy entanglement and superconducting single-photon detectors to detect the photon pairs after 100 km. We also demonstrate that the distributed photon pairs can still be useful for quantum key distribution and other quantum communication tasks.
We develop a one-step scheme for generating multiparticle entangled states between two cold atomic clouds in distant cavities coupled by an optical fiber. We show that, through suitably choosing the intensities and detunings of the fields and precisely tuning the time evolution of the system, multiparticle entanglement between the separated atomic clouds can be engineered deterministically, in which quantum manipulations are insensitive to the states of the cavity and losses of the fiber. The experimental feasibility of this scheme is analyzed based on recent experimental advances in the reali…
Generation of two-photon wavepackets, produced by spontaneous parametric down conversion in crystals with linearly chirped quasi-phase matching grating, is analyzed. Although being spectrally broad, two-photon wavepackets produced this way are not Fourier transform limited. In the paper we discuss the temporal compression of the wavepackets, exploiting the insertion of a standard optical fiber in the path of one of the two photons. The effect is analyzed by means of full numerical calculation and the exact dispersion dependencies in both the crystal and the fiber are considered. The study open…
A scheme for the implementation of the cluster state model of quantum computing in optical fibers, which enables the feedforward feature, is proposed. This scheme uses the time-bin encoding of qubits. Following previously suggested methods of applying arbitrary one-qubit gates in optical fibers, two different ways for the realization of fusion gate types I and II for cluster production are proposed: a fully time-bin based encoding scheme and a combination of time-bin and polarization based encoding scheme. Also the methods of measurement in any desired bases for the purpose of the processing o…
Tapered optical fibers with a nanofiber waist are versatile tools for interfacing light and matter. In this context, laser-cooled atoms trapped in the evanescent field surrounding the optical nanofiber are of particular interest: They exhibit both long ground-state coherence times and efficient coupling to fiber-guided fields. Here, we demonstrate electromagnetically induced transparency, slow light, and the storage of fiber-guided optical pulses in an ensemble of cold atoms trapped in a nanofiber-based optical lattice. We measure a slow-down of light pulses to group velocities of 50 m/s. More…
The optical implementation of the recently proposed unambiguous identification of coherent states is presented. Our system works as a programmable discriminator between two, in general non-orthogonal weak coherent states. The principle of operation lies in the interference of three light beams - two program states and one unknown coherent state which can be equal to whichever of the two program states. The experiment is based on fiber optics. Its results confirm theoretical predictions and the experimental setup can be straightforwardly extended for higher numbers of program states.
With a view to quantum foundations, we define the concepts of an empirical model (a probabilistic model describing measurements and outcomes), a hidden-variable model (an empirical model augmented by unobserved variables), and various properties of hidden-variable models, for the case of infinite measurement spaces and finite outcome spaces. Thus, our framework is general enough to include, for example, quantum experiments that involve spin measurements at arbitrary relative angles. Within this framework, we use the concept of the fiber product of measures to prove general versions of two dete…
Quantum Key Distribution (QKD) allows distant parties to exchange cryptographic keys with unconditional security by encoding information on the degrees of freedom of photons. Polarization encoding has been extensively used in QKD implementations along free-space, optical fiber and satellite-based links. However, the polarization encoders used in such implementations are unstable, expensive, complex and can even exhibit side-channels that undermine the security of the implemented protocol. Here we propose a self-compensating polarization encoder based on a Lithium Niobate phase modulator inside…
We have experimentally realized a technique to generate, control and measure entangled qutrits, 3-dimensional quantum systems. This scheme uses spontaneous parametric down converted photons and unbalanced 3-arm fiber optic interferometers in a scheme analogous to the Franson interferometric arrangement for qubits. The results reveal a source capable of generating maximally entangled states with a net state fidelity, F = 0.985 $\pm$ 0.018. Further the control over the system reveals a high, net, 2-photon interference fringe visibility, V = 0.919 $\pm$ 0.026. This has all been done at telecom wa…
Three related topics on the quantum-vacuum geometric phases in a noncoplanarly curved optical fiber is presented: (i) a brief review: the investigation of vacuum effect and its experimental realization; (ii) the sequence of ideas of geometric phases in the fiber; (iii) three derivations of effective Hamiltonian that describes the wave propagation of photon field in a curved fiber.
We report the first experimental realization of entanglement swapping over large distances in optical fibers. Two photons separated by more than two km of optical fibers are entangled, although they never directly interacted. We use two pairs of time-bin entangled qubits created in spatially separated sources and carried by photons at telecommunication wavelengths. A partial Bell state measurement is performed with one photon from each pair which projects the two remaining photons, formerly independent onto an entangled state. A visibility high enough to violate a Bell inequality is reported, …
We present the experimental realization of a quantum fiber-pigtail. The device consists of a semiconductor quantum-dot embedded into a conical photonic wire that is directly connected to the core of a fiber-pigtail. We demonstrate a photon collection efficiency at the output of the fiber of 5.8% and suggest realistic improvements for the implementation of a useful device in the context of quantum information. We finally discuss potential applications in scanning probe microscopy.
Realizing a strong interaction between individual optical photons is an important objective of research in quantum science and technology. Since photons do not interact directly, this goal requires, e.g., an optical medium in which the light experiences a phase shift that depends nonlinearly on the photon number. Once the additional phase shift for two photons reaches pi, such an ultra-strong nonlinearity could even enable the direct implementation of high-fidelity quantum logic operations. However, the nonlinear response of standard optical media is many orders of magnitude too weak for this …
Practical quantum networking architectures are crucial for scaling the connection of quantum resources. Yet quantum network testbeds have thus far underutilized the full capabilities of modern lightwave communications, such as flexible-grid bandwidth allocation. In this work, we implement flex-grid entanglement distribution in a deployed network for the first time, connecting nodes in three distinct campus buildings time-synchronized via the Global Positioning System (GPS). We quantify the quality of the distributed polarization entanglement via log-negativity, which offers a generic metric of…
We present the realization of a combined trapped-ion and optical cavity system, in which a single Yb^+ ion is confined by a micron-scale ion trap inside a 230 mum-long optical fiber cavity. We characterize the spatial ion-cavity coupling and measure the ion-cavity coupling strength using a cavity-stimulated Lambda-transition. Owing to the small mode volume of the fiber resonator, the coherent coupling strength between the ion and a single photon exceeds the natural decay rate of the dipole moment. This system can be integrated into ion-photon quantum networks and is a step towards cavity quant…
We experimentally demonstrate stable and user-adjustable single-photon interference in a 1 km long fiber- optical Mach-Zehnder interferometer, using an active phase control system with the feedback provided by a classical laser. We are able to continuously tune the single-photon phase difference between the interferometer arms using a phase modulator, which is synchronized with the gate window of the single-photon detectors. The phase control system employs a piezoelectric fiber stretcher to stabilize the phase drift in the interferometer. A single-photon net visibility of 0.97 is obtained, yi…
Quantum information science breaks limitations of conventional information transfer, cryptography and computation by using quantum superpositions or entanglement as resources for information processing. Here, we report on the experimental realization of three-party quantum communication protocols using single three-level quantum system (qutrit) communication: secret sharing, detectable Byzantine agreement, and communication complexity reduction for a three-valued function. We have implemented these three schemes using the same optical fiber interferometric setup. Our realization is easily scal…
We perform extended numerical studies to maximize the overall photon coupling efficiency of fiber-coupled quantum dot single-photon sources emitting in the near-infrared and telecom regime. Using the finite element method, we optimize the photon extraction and fiber-coupling efficiency of quantum dot single-photon sources based on micromesas, microlenses, circular Bragg grating cavities and micropillars. The numerical simulations which consider the entire system consisting of the quantum dot source itself, the coupling lens, and the single-mode fiber yield overall photon coupling efficiencies …
A long distance quantum teleportation experiment with a fiber-delayed Bell State Measurement (BSM) is reported. The source creating the qubits to be teleported and the source creating the necessary entangled state are connected to the beam splitter realizing the BSM by two 2 km long optical fibers. In addition, the teleported qubits are analyzed after 2,2 km of optical fiber, in another lab separated by 55 m. Time bin qubits carried by photons at 1310 nm are teleported onto photons at 1550 nm. The fidelity is of 77%, above the maximal value obtainable without entanglement. This is the first re…
Wave propagation on the surface of cylinders exhibits interferometric self imaging, much like the Talbot effect in the near-field diffraction at periodic gratings. We report the experimental observation of the cylindrical Talbot carpet in weakly-guiding ring-core fibers for classical light fields. We further show that the ring-core fiber acts as a high-order optical beamsplitter for single photons, whose output can be controlled by the relative phase between the input light fields. By also demonstrating high-quality two-photon interference between indistinguishable photons sent into the ring-c…
We present an experimental realization of a quantum digital signature protocol which, together with a standard quantum key distribution link, increases transmission distance to kilometre ranges, three orders of magnitude larger than in previous realizations. The bit-rate is also significantly increased compared with previous quantum signature demonstrations. This work illustrates that quantum digital signatures can be realized with optical components similar to those used for quantum key distribution, and could be implemented in existing optical fiber networks.
We present the experimental realization of optimal symmetric and asymmetric phase-covariant 1->2 cloning of qubit states using fiber optics. State of each qubit is encoded into a single photon which can propagate through two optical fibers. The operation of our device is based on one- and two-photon interference. We have demonstrated creation of two copies of any state of a qubit from the equator of the Bloch sphere. The measured fidelities of both copies are close to the theoretical values and they surpass the theoretical maximum obtainable with the universal cloner.
Interference and coincidence detection of two photons emitted by two remote ions can lead to an entangled state which is a critical resource for scalable quantum information processing. Currently, the success probabilities of experimental realizations of this protocol are mainly limited by low coupling efficiency of a photon emitted by an ion into a single mode fiber. Here, we consider two strategies to enhance the collection probability of a photon emitted from a trapped Yb ion, using analytic methods that can be easily applied to other types of ion or neutral atoms. Our analysis shows that w…
We present an experimental realization of a robust quantum communication scheme [Phys. Rev. Lett. 93, 220501 (2004)] using pairs of photons entangled in polarization and time. Our method overcomes errors due to collective rotation of the polarization modes (e.g., birefringence in optical fiber or misalignment), is insensitive to the phase's fluctuation of the interferometer, and does not require any shared reference frame including time reference, except the need to label different photons. The practical robustness of the scheme is further shown by implementing a variation of the Bennett-Brass…
Realization of integrated photonic circuits on a single chip requires controlled manipulation and integration of solid-state quantum emitters with nanophotonic components. Previous works focused on emitters embedded in a three-dimensional crystals -- such as nanodiamonds or quantum dots. In contrast, in this work we demonstrate coupling of a single emitter in a two-dimensional (2D) material, namely hexagonal boron nitride (hBN), with a tapered optical fiber and find a collection efficiency of the system is found to be 10~\%. Furthermore, due to the single dipole character of the emitter, we we…
The effect of boundary deformation on the non-separable entanglement which appears in the classical elec- tromagnetic field is considered. A quantum chaotic billiard geometry is used to explore the influence of a mechanical modification of the optical fiber cross-sectional geometry on the production of non-separable entan- glement within classical fields. For the experimental realization of our idea, we propose an optical fiber with a cross section that belongs to the family of Robnik chaotic billiards. Our results show that a modification of the fiber geometry from a regular to a chaotic regi…
Nitrogen-vacancy (NV) quantum magnetometers offer exceptional sensitivity and long-term stability. However, their use to date in distributed sensing applications, including remote detection of ferrous metals, geophysics, and biosensing, has been limited due to the need to combine optical, RF, and magnetic excitations into a single system. Existing approaches have yielded localized devices but not distributed capabilities. In this study, we report on a continuous system-in-a-fiber architecture that enables distributed magnetic sensing over extended lengths. Key to this realization is a thermall…
We demonstrate the fabrication of ultra-low-loss, all-fiber Fabry-Pérot cavities containing a nanofiber section, optimized for cavity quantum electrodynamics. By continuously monitoring the finesse and fiber radius during fabrication of a nanofiber between two fiber Bragg gratings, we are able to precisely evaluate taper transmission as a function of radius. The resulting cavities have an internal round-trip loss of only 0.31% at a nanofiber waist radius of 207 nm, with a total finesse of 1380, and a maximum expected internal cooperativity of $\sim$ 1050 for a cesium atom on the nanofiber surf…
Realization of quantum photonic devices requires coupling single quantum emitters to the mode of optical resonators. In this work we present a hybrid system consisting of defect centers in few-layer hBN grown by chemical vapor deposition and a fiber-based Fabry-Perot cavity. The sub 10 nm thickness of hBN and its smooth surface enables efficient integration into the cavity mode. We operate our hybrid platform over a broad spectral range larger than 30 nm and use its tuneability to explore different coupling regimes. Consequently, we achieve very large cavity-assisted signal enhancement up to 5…
Photon-based quantum information processing promises new technologies including optical quantum computing, quantum cryptography, and distributed quantum networks. Polarization-encoded photons at telecommunication wavelengths provide a compelling platform for practical realization of these technologies. However, despite important success towards building elementary components compatible with this platform, including sources of entangled photons, efficient single photon detectors, and on-chip quantum circuits, a missing element has been atomic quantum memory that directly allows for reversible m…
Optical nonreciprocity is important in photonic information processing to route the optical signal or prevent the reverse flow of noise. By adopting the strong nonlinearity associated with a few atoms in a strongly coupled cavity QED system and an asymmetric cavity configuration, we experimentally demonstrate the nonreciprocal transmission between two counterpropagating light fields with extremely low power. This nonreciprocity can even occur on a few-photon level due to the high optical nonlinearity of the system. The working power can be flexibly tuned by changing the effective number of ato…
