Optical quantum information processing and storage

Wafer-level flexible carbon-based film for fluorescent display and optical information storage

Quantum memories enabling the storage of an input photonic qubit and its later retrieval with a fidelity beating any classical device constitute essential components in quantum communication networks and optical quantum information processing [1]. Our main goal is to develop a new generation of memories which have a near-unity efficiency for storage-and-retrieval operations, as well as high multiplexing capabilities. In the recent years, we demonstrated for instance the implementation for quantum bits encoded in the orbital angular momentum degree of freedom, which provides an essential capability for future networks with multimode capability [2]. We also realized multiple-degree-of-freedom memory, which can find applications in classical data processing but also in quantum network scenarios where states structured in phase and polarization have been shown to provide promising attributes [3].

A high-fidelity source of identical single photons is essential for numerous\nquantum technologies such as quantum repeaters and optical quantum information\nprocessing. Hallmarks thereof are a near-unity single-photon purity, near-unity\nindistinguishability of consecutively emitted photons, and high brightness\nthrough a near-unity number of photons per time bin. In order to embed such\nsources in quantum networks, optical fiber integration is essential but\ncomplicated by cryogenic compatability and noise. Here we demonstrate a\nresonantly pumped, quantum dot (QD) based, transmission operated, single-mode\nfiber coupled single photon source with a purity of 97%, indistinguishability\nof 90%, and a brightness of 17%. This is achieved by deploying a unique\nmicropillar cavity design in a closed-cycle cryostat, which is operated using a\nthrough-fiber cross-polarization technique to remove the pump laser light from\nthe resonantly scattered single photons. These results pave the way for fully\nfiber integrated photonic quantum networks, as our technology is equally\napplicable for cavity-QED based photonic quantum gates.\n

Dielectric four-port devices play an important role in optical quantum information processing. Since for causality reasons the permittivity is a complex function of frequency, dielectrics are typical examples of noisy quantum channels, which cannot preserve quantum coherence. To study the effects of quantum decoherence, we start from the quantized electromagnetic field in an arbitrary Kramers--Kronig dielectric of given complex permittivity and construct the transformation relating the output quantum state to the input quantum state, without placing restrictions on the frequency. We apply the formalism to some typical examples in quantum communication. In particular we show that for entangled qubits the Bell-basis states $|\Psi^\pm>$ are more robust against decoherence than the states $|\Phi^\pm>$.

Quantum information offers the promise of being able to perform certain communication and computation tasks that cannot be done with conventional information technology (IT). Optical Quantum Information Processing (QIP) holds particular appeal, since it offers the prospect of communicating and computing with the same type of qubit. Linear optical techniques have been shown to be scalable, but the corresponding quantum computing circuits need many auxiliary resources. Here we present an alternative approach to optical QIP, based on the use of weak cross-Kerr nonlinearities and homodyne measurements. We show how this approach provides the fundamental building blocks for highly efficient non-absorbing single photon number resolving detectors, two qubit parity detectors, Bell state measurements and finally near deterministic control-not (CNOT) gates. These are essential QIP devices

Coherent control of optical solitons interaction via external potential in electromagnetically induced transparency system

Nondestructive two-photon parity detector with near unity efficiency

In optical quantum information processing with continuous variables, optical non-Gaussian quantum states are essential for universal and fault-tolerant quantum computation. Experimentally, their most typical generation method is photon subtraction (PS), where single-photon detection by an on/off detector probabilistically heralds the generation of squeezed single-photon states. In PS, however, trying to avoid unwanted multiphoton detection inevitably limits the generation rate, hindering the application of squeezed single-photon states. Here, we theoretically show that generalized photon subtraction (GPS), a simple extension of PS, can improve the generation rate while maintaining the quality of the generated states. Furthermore, we experimentally demonstrate the generation rate improvement for 2-dB- and 4-dB-squeezed single-photon states compared to PS, by more than one order of magnitude, particularly for the case of 2 dB. Our results will accelerate the application of squeezed single-photon states to more advanced quantum information protocols.

Solid-state sources of single-photon emitters are highly desired for scalable quantum photonic applications, such as quantum communication, optical quantum information processing, and metrology. In the past year, great strides have been made in the characterization of single defects in wide-bandgap materials, such as silicon carbide and diamond, as well as single molecules, quantum dots, and carbon nanotubes. More recently, single-photon emitters in layered van der Waals materials attracted tremendous attention, because the two-dimensional (2D) lattice allows for high photon extraction efficiency and easy integration into photonic circuits. In this review, we discuss recent advances in mastering single-photon emitters in 2D materials, electrical generation pathways, detuning, and resonator coupling towards use as quantum light sources. Finally, we discuss the remaining challenges and the outlooks for layered material-based quantum photonic sources.

Spatial confinement of quantum excitations on their characteristic wavelength scale in low dimensional materials offers unique possibilities to engineer the electronic structure and thereby control their physical properties by way of simple manipulation of geometrical parameters. This has led to an overwhelming interest in quasi-zero dimensional semiconductors or quantum dots as tunable materials for multitude of exciting applications in optoelectronic and nonlinear optical devices and quantum information processing. Large nonlinear optical response and high luminescence quantum yield expected in these systems is a consequence of huge enhancement of transition probabilities ensuing from quantum confinement. High quantum efficiency of photoluminescence, however, is not usually realized in the case of bare semiconductor nanoparticles owing to the presence of surface states. In this talk, I will focus on the role of quantum confinement and surface states in ascertaining nonlinear optical and optoelectronic properties of II–VI semiconductor quantum dots and their nanocomposites. I will also discuss the influence of nonlinear optical processes on their optoelectronic characteristics.

Bi-activated MgGa2O4 phosphors with rich defect energy levels: Spectral property and optical storage applications

The introduction of advanced optical materials into communication technology facilitates increased data trans-mission speed, increased bandwidth, intrinsic low crosstalk and high security in multiplexed systems, and simplified implementation of parallel processing. Prototype and first-generation optical communication, information storage and information processing systems have been developed from hybrid electro-optical or all-optical effects in inorganic crystals and semiconductors. Organic and polymer nonlinear optical materials may have processing or performance ad-vantages in the next generation of optical information systems design, but research is needed to define the materials of interest and development will be necessary to incorporate these new materials into practical active elements. This paper is an overview of 3M's program for development of nonlinear optical materials.

Semiconductor photodetectors at1550nm wavelengths have been widely used in free space optical communications, sensing, infrared imaging, and quantum information processing. These detectors require high sensitivity with high detection efficiency and a large dynamic range. But for fundamental material and device limits, all these performances cannot be achieved in a single device under the same operating conditions. To overcome this bottleneck, we integrate three coupled gain mechanisms in a single element device, operating below breakdown to obtain a high net gain and at the same time utilize the negative feedback mechanism to minimize the gain fluctuation. This results in an improved signal to noise ratio, which is the key to obtaining a superior sensitivity. Integration of gain mechanisms in an InP-InGaAs device was analytically modeled and experimentally demonstrated.

Optical vortices, which are beams with spiral‐shaped wavefronts and screw phase dislocations, have potential for supporting high‐capacity optical communications. In this study, the generation of 1D and 2D vortex‐beam arrays is theoretically proposed and experimentally demonstrated by introducing novel forked‐photonic lattices in a three‐level 85Rb atomic medium. Such forked‐photonic lattices are established through the interference of Gaussian and vortex coupling beams. The input Gaussian probe beam that travels through this lattice experiences phase superposition and is diffracted into vortex‐beam arrays. Moreover, the relative efficiency of the high‐order diffractions can be enhanced by tuning the two‐photon detuning and power of the coupling beams. The enriched diffractive arrays of a vortex probe beam propagating in such forked‐photonic lattices are also presented. The experimental results agree well with those of the numerical simulations. This work suggests that atomic systems are a fertile platform for creating and controlling vortex‐beam arrays, and that they can shed light on ongoing exploration in the fields of optical manipulation and quantum information processing.

The programmable photonic integrated circuit (PIC) is an enabling technology behind optical interconnects and quantum information processing. Conventionally, the programmability of PICs is driven by the thermo-optic effect, free carrier dispersion, or mechanical tuning. These effects afford either high speed or a large extinction ratio, but all require constant power or bias to maintain the states, which is undesirable for programmability with infrequent switching. Recent progress in programmable PICs based on nonvolatile phase-change materials (PCMs) offers an attractive solution to a truly "set-and-forget" switch that requires zero static energy. Here, we report an essential building block of large-scale programmable PICs─a racetrack resonator with independent control of coupling and phase. We changed the resonance extinction ratio (ER) without perturbing the resonance wavelength, leveraging a programmable unit based on a directional coupler and a low-loss PCM Sb2Se3. The unit is only 33-μm-long and has an operating bandwidth over 50 nm, a low insertion loss (∼0.36 dB), high ER (∼15 dB), and excellent fabrication yield of over 1000 cycles endurance across nine switches. The work is a crucial step toward future large-scale energy-efficient programmable PICs.