No description available.

No description available.

No description available.

Thesis (Ph.D.)--Australian National University, 2001.

No description available.

The performance of optical measurement systems is ultimately limited by the quantum nature of light. In this thesis, two techniques for circumventing the standard quantum measurement limits are modelled and tested experimentally. These techniques are electro-optic control and the use of squeezed light. An optical parametric amplifier is used to generate squeezing at 1064nm. The parametric amplifier is pumped by the output of a second harmonic generation cavity, which in turn is pumped by a Nd:YAG laser. By using various frequency locking techniques, the quadrature phase of the squeezing is stabilised, therefore making our squeezed source suitable for long term measurements. The best recorded squeezing is 5.5dB (or 70\%) below the standard quantum limit. The stability of our experiment makes it possible to perform a time domain measurement of photocurrent correlations due to squeezing. This technique allows direct visualisation of the quantum correlations caused by squeezed light. On the road to developing our squeezed source, methods of frequency locking optical cavities are investigated. In particular, the tilt locking method is tested on the second harmonic generation cavity used in the squeezing experiment. The standard method for locking this cavity involves the use of modulation sidebands, therefore leading to a noisy second harmonic wave. The modulation free tilt-locking method, which is based on spatial mode interference, is shown to be a reliable alternative. In some cases, electro-optic control may be used to suppress quantum measurement noise. Electro-optic feedback is investigated as a method for suppressing radiation pressure noise in an optical cavity. Modelling shows that the `squashed' light inside a feedback loop can reduce radiation pressure noise by a factor of two below the standard quantum limit. This result in then applied to a thermal noise detection system. The reduction in radiation pressure noise is shown to give improved thermal noise sensitivity, therefore proving that the modified noise properties of light inside a feedback loop can be used to reduce quantum measurement noise. Another method of electro-optic control is electro-optic feedforward. This is also investigated as a technique for manipulating quantum measurements. It is used to achieve noiseless amplification of a phase quadrature signal. The results clearly show that a feedforward loop is a phase sensitive amplifier that breaks the quantum limit for phase insensitive amplification. This experiment is the first demonstration of noiseless phase quadrature amplification. Finally, feedforward is explored as a tool for improving the performance of quantum nondemolition measurements. Modelling shows that feedforward is an effective method of increasing signal transfer efficiency. Feedforward is also shown to work well in conjunction with meter squeezing. Together, meter squeezing and feedforward provide a comprehensive quantum nondemolition enhancement package. Using the squeezed light from our optical parametric amplifier, an experimental demonstration of the enhancement scheme is shown to achieve record signal transfer efficiency of $T_{s}+T_{m}=1.81$.

Thesis (M.S.)--Rutgers University, 2007. / "Graduate Program in Electrical and Computer Engineering." Includes bibliographical references (p. 259-263).

Photons are robust carriers of quantum information as they can propagate long distances without losing quantum entanglement and coherence. Compared to quantum information in matter-based carriers, such as superconducting oscillators, trapped ions and atoms, quantum dots, and vacancy centers in crystals, the photonic quantum states are robust against perturbations from the environment, such as parasitic electromagnetic fields and thermal fluctuations (phonons), making it an ideal candidate for room-temperature-based quantum metrology and information processing applications. Such robustness is due to photon-photon scattering in the vacuum being extremely improbable and photon-atom interactions being in the linear regime for most materials. Nevertheless, photon-photon or photon-atom nonlinear interactions are also critical for all quantum photonic applications as nonlinearity is required for generating non-classical states of light. Furthermore, nonlinear interactions greatly expand the variety of Hamiltonian that can be engineered for a given system or subsystem, which is a direct measure of the system's functionality. Thus, the ability to engineer nonlinear interactions has been one of the primary research focuses in quantum photonics. This thesis presents research on using nonlinear photonic chips to harness the unique properties offered by quantum mechanics, with applications in precision metrology and information procession. Atoms possess a rich set of quantum properties that have no counterparts in the classical world. Even in warm vapor form, atomic gases maintain sufficient coherence for tasks, including time keeping, electric field sensing and quantum memories. We develop chip-based light sources that can interact with narrow-band atomic transitions in order to miniaturize these applications. Typical Alkali atoms have transition around the visible light regime, where photonic materials exhibit strong normal group-velocity dispersion (GVD) which inhibits light generation via nonlinear interactions. We offer a systematic solution by re-examining the dispersion engineer techniques, which revealed that higher-order waveguide modes can have stronger anomalous GVD. With this technique, we demonstrate on-chip mode-locked pulses (Kerr combs) at a record-low wavelength, which can be used for high-precision atomic clocks. We also develop chip-based narrow-band high-brightness photon sources at the visible regime using nonlinear interactions. Such photons can interact with atom-based quantum memories and gates, which can find applications in both quantum communication and computation. Squeezed state is also an important class of non-classical states with key applications in quantum metrology, quantum simulation, and continuous-variable quantum information processing. Typically, squeezed states are generated using χ² processes, which are not readily available on most photonic platforms. For the first time, we demonstrate squeezed state generation using a dual-pumped four-wave-mixing process, which we implement on a silicon-nitride chip. To perform quantum simulation or computation with squeezed states, we need programmable interferometer arrays and photon-number resolving (PNR) detectors. Current PNR detectors rely on superconducting effects which require Kelvin level temperatures. We propose a room-temperature PNR scheme based on optical nonlinearity. We show that using cascaded χ² interactions, a single photon can impart an observable phase on a probe beam, which can be implemented within the current fabrication capabilities. Our squeezed-state-generation and PNR-detection devices lay a practical path towards room-temperature quantum simulation and computing.

In this thesis, we report the observations of optical squeezing from second harmonic generation (SHG), optical parametric oscillation (OPO) and optical parametric amplification (OPA). Demonstrations and proposals of applications involving the squeezed light and electro-optic control loops are presented. ¶ In our SHG setup, we report the observation of 2.1 dB of intensity squeezing on the second harmonic (SH) output. Investigations into the system show that the squeezing performance of a SHG system is critically affected by the pump noise and a modular theory of noise propagation is developed to describe and quantify this effect. Our experimental data has also shown that in a low-loss SHG system, intra-cavity nondegenerate OPO modes can simultaneously occur. This competition of nonlinear processes leads to the optical clamping of the SH output power and in general can degrade the SH squeezing. We model this competition and show that it imposes a limit to the observable SH squeezing. Proposals for minimizing the effect of competition are presented. ¶ In our OPO setup, we report the observation of 7.1 dB of vacuum squeezing and more than 4 dB of intensity squeezing when the OPO is operating as a parametric amplifier. We present the design criteria and discuss the limits to the observable squeezing from the OPO.We attribute the large amount of squeezing obtained in our experiment to the high escape efficiency of the OPO. The effect of phase jitter on the squeezing of the vacuum state is modeled. ¶ The quantum noise performance of an electro-optic feedforward control loop is investigated. With classical coherent inputs, we demonstrate that vacuum fluctuations introduced at the beam splitter of the control loop can be completely cancelled by an optimum amount of positive feedforward. The cancellation of vacuum fluctuations leads to the possibility of noiseless signal amplification with the feedforward loop. Comparison shows that the feedforward amplifier is superior or at least comparable in performance with other noiseless amplification schemes. When combined with an injection-locked non-planar ring Nd:YAG laser, we demonstrate that signal and power amplifications can both be noiseless and independently variable. ¶ Using squeezed inputs to the feedforward control loop, we demonstrate that information carrying squeezed states can be made robust to large downstream transmission losses via a noiseless signal amplification. We show that the combination of a squeezed vacuum meter input and a feedforward loop is a quantum nondemolition (QND) device, with the feedforward loop providing an additional improvement on the transfer of signal. In general, the use of a squeezed vacuum meter input and an electro-optic feedforward loop can provide pre- and post- enhancements to many existing QND schemes. ¶ Finally, we proposed that the quantum teleportation of a continuous-wave optical state can be achieved using a pair of phase and amplitude electro-optic feedforward loops with two orthogonal quadrature squeezed inputs. The signal transfer and quantum correlation of the teleported optical state are analysed. We show that a two dimensional diagram, similar to the QND figures of merits, can be used to quantify the performance of a teleporter.

The primary study of this thesis is spin-nematic squeezing in a spin-1 condensate. The measurement of spin-nematic squeezing builds on the success of previous experiments of spin-mixing together with advances in low noise atom counting. The major contributions of this thesis are linking theoretical models to experimental results and the development of the intuition and tools to address the squeezed subspaces. Understanding how spin-nematic squeezing is generated and how to measure it has required a review of several theoretical models of spin-mixing as well as extending these existing models. This extension reveals that the squeezing is between quadratures of a spin moment and a nematic (quadrapole) moment in abstract subspaces of the SU(3) symmetry group of the spin-1 system. The identification of the subspaces within the SU(3) symmetry allowed the development of techniques using RF and microwave oscillating magnetic fields to manipulate the phase space in order to measure the spin-nematic squeezing. Spin-mixing from a classically meta-stable state, the phase space manipulation, and low noise atom counting form the core of the experiment to measure spin-nematic squeezing. Spin-nematic squeezing is also compared to its quantum optics analogue, two-mode squeezing generated by four-wave mixing. The other experimental study in this thesis is performing spin-dependent photo-association spectroscopy. Spin-mixing is known to depend on the difference of the strengths of the scattering channels of the atoms. Optical Feshbach resonances have been shown to be able to alter these scattering lengths but with prohibitive losses of atoms near the resonance. The possibility of using multiple nearby resonances from different scattering channels has been proposed to overcome this limitation. However there was no spectroscopy in the literature which analyzes for the different scattering channels of atoms for the same initial states. Through analysis of the initial atomic states, this thesis studies how the spin state of the atoms affects what photo-association resonances are available to the colliding atoms based on their scattering channel and how this affects the optical Feshbach resonances. From this analysis a prediction is made for the extent of alteration of spin-mixing achievable as well as the impact on the atom loss rate.