Alastair G. Sinclair

Metrology of single-photon sources and detectors: a review

Abstract. The generation, measurement, and manipulation of light at the single- and few-photon levels underpin a rapidly expanding range of applications. These range from applications moving into the few-photon regime in order to achieve improved sensitivity and/or energy efficiency, as well as new applications that operate solely in this regime, such as quantum key distribution and physical quantum random number generation. There is intensive research to develop new quantum optical technologies, for example, quantum sensing, simulation, and computing. These applications rely on the performance of the single-photon sources and detectors they employ; this review article gives an overview of the methods, both conventional and recently developed, that are available for measuring the performance of these devices, with traceability to the SI system.

A monolithic array of three-dimensional ion traps fabricated with conventional semiconductor technology

The coherent control of quantum-entangled states of trapped ions has led to significant advances in quantum information, quantum simulation, quantum metrology and laboratory tests of quantum mechanics and relativity. All of the basic requirements for processing quantum information with arrays of ion-based quantum bits (qubits) have been proven in principle. However, so far, no more than 14 ion-based qubits have been entangled with the ion-trap approach, so there is a clear need for arrays of ion traps that can handle a much larger number of qubits. Traps consisting of a two-dimensional electrode array have undergone significant development, but three-dimensional trap geometries can create a superior confining potential. However, existing three-dimensional approaches, as used in the most advanced experiments with trap arrays, cannot be scaled up to handle greatly increased numbers of ions. Here, we report a monolithic three-dimensional ion microtrap array etched from a silica-on-silicon wafer using conventional semiconductor fabrication technology. We have confined individual (88)Sr(+) ions and strings of up to 14 ions in a single segment of the array. We have measured motional frequencies, ion heating rates and storage times. Our results demonstrate that it should be possible to handle several tens of ion-based qubits with this approach.

Monolithic microfabricated ion trap chip design for scaleable quantum processors

A design is proposed for a novel ion trap quantum processor chip, microfabricated using a process based on planar silica-on-silicon techniques. The trap electrodes are of gold-coated silica and are spaced by highly doped silicon in a monolithic structure. This design allows a unit aspect-ratio trap with an ion-electrode separation below 100 μm, when using current fabrication techniques. The trapping potential is modelled and the operating parameters required to achieve motional frequencies of a few MHz are calculated. RF loss and the resultant heating of the trap chip are not found to be a factor limiting the traps operation. This monolithic unit aspect-ratio trap is therefore expected to exhibit a deep potential well, high trap efficiency, and a low RF loss, when compared to other microfabricated traps. This technological approach is in principle scaleable to complex devices, and may form the basis for large-scale ion trap quantum processors.

Field trial of a quantum secured 10 Gb/s DWDM transmission system over a single installed fiber

We present results from the first field-trial of a quantum-secured DWDM transmission system, in which quantum key distribution (QKD) is combined with 4 × 10 Gb/s encrypted data and transmitted simultaneously over 26 km of field installed fiber. QKD is used to frequently refresh the key for AES-256 encryption of the 10 Gb/s data traffic. Scalability to over 40 DWDM channels is analyzed.

Accurate and agile digital control of optical phase, amplitude and frequency for coherent atomic manipulation of atomic systems

We demonstrate a system for fast and agile digital control of laser phase, amplitude and frequency for applications in coherent atomic systems. The full versatility of a direct digital synthesis radiofrequency source is faithfully transferred to laser radiation via acousto-optic modulation. Optical beatnotes are used to measure phase steps up to 2π, which are accurately implemented with a resolution of ≤ 10 mrad. By linearizing the optical modulation process, amplitude-shaped pulses of durations ranging from 500 ns to 500 ms, in excellent agreement with the programmed functional form, are demonstrated. Pulse durations are limited only by the 30 ns rise time of the modulation process, and a measured extinction ratio of > 5 × 10(11) is achieved. The system presented here was developed specifically for controlling the quantum state of trapped ions with sequences of multiple laser pulses, including composite and bichromatic pulses. The demonstrated techniques are widely applicable to other atomic systems ranging across quantum information processing, frequency metrology, atom interferometry, and single-photon generation.

Fabrication of a Monolithic Array of Three Dimensional Si-based Ion Traps

Segmented linear ion trap arrays are versatile devices that are increasingly used to study quantum physics and demonstrate the fundamental principles of quantum information processing. Traps with three-dimensional (3-D) electrode geometries can create a superior confining potential for ions. However, the realization of a monolithic 3-D microchip trap with scalable fabrication technology remains challenging. In this paper the microfabrication of a monolithic array of 3-D ion microtraps in a semiconductor chip is presented. The electrode structure is formed by micromachining a silica-on-silicon wafer and metallizing the dielectric with gold. The fabrication method uses conventional semiconductor wafer processing tools and techniques. The specific operating characteristics which demonstrate the suitability of the chosen material system and fabrication process are presented.

Optimum measurement strategies for trapped ion optical frequency standards

The experimental parameters required in order to maximize the stability of a single-ion based optical clock are analysed. This stability is a trade-off between on the one hand the steepness of the discriminant signal derived from the laser excitation of the ion and on the other the binomial noise associated with the excitation of a single particle. Optimum conditions are found for both Rabi and Ramsey excitation of the clock transition.

Optical-clock local-oscillator stabilization scheme

Stabilization of a laser to an optical-clock transition has been demonstrated using Ramseys phase-modulation technique. The technique was implemented using a 674 nm laser and a component of the 5 s 2S1/2 → 4d 2D5/2 optical clock transition in a single 88Sr+ ion. The lock performance observed was consistent with the short-term stability of the local oscillator. Compared with existing frequency-modulation stabilization schemes, this technique offers advantages for use in single-ion optical clocks through its possible increased resolution and the ability to conveniently compensate known systematic shifts.

Wide spectral range confocal microscope based on endlessly single-mode fiber.

We report an endlessly single mode, fiber-optic confocal microscope, based on a large mode area photonic crystal fiber. The microscope confines a very broad spectral range of excitation and emission wavelengths to a single spatial mode in the fiber. Single-mode operation over an optical octave is feasible. At a magnification of 10 and λ = 900 nm, its resolution was measured to be 1.0 μm (lateral) and 2.5 μm (axial). The microscopes use is demonstrated by imaging single photons emitted by individual InAs quantum dots in a pillar microcavity.

Measurements of statistical properties of single photons emitted by a solitary NV centre in synthetic diamond

This paper reports on a study of the statistical properties of single photons emitted by a nitrogen vacancy centre using a confocal microscope and Hanbury-Brown and Twiss interferometer. High signal-to-noise photon correlation histograms from a single NV centre have been recorded for various pump laser powers. The form of these signals can be described by modelling the nitrogen vacancy as a three-level system. The parameters that characterize the model have been measured as a function of pump laser power.