Bulletin of the American Physical Society
2007 APS March Meeting
Volume 52, Number 1
Monday–Friday, March 5–9, 2007; Denver, Colorado
Session A33: Focus Session: Quantum-Limited Measurements |
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Sponsoring Units: GQI DAMOP Chair: Matthew Leifer, University of Waterloo / Perimeter Institute Room: Colorado Convention Center 403 |
Monday, March 5, 2007 8:00AM - 8:36AM |
A33.00001: Quantum-Limited and Ultra-Precision Measurements Invited Speaker: I will provide a brief overview of the current state of the field of experimental quantum-limited measurements. In particular I will focus on the role of entanglement in metrology and quantum parameter estimation for achieving fundamental uncertainty limits established by quantum mechanics. In addition to summarizing the state of the art as this pertains to experimental implementations, I will conclude by discussing a current proposal to improve existing quantum metrological techniques by exploiting multi-body quantum interactions. [Preview Abstract] |
Monday, March 5, 2007 8:36AM - 8:48AM |
A33.00002: Assessing the Quality of Quantum Sensors Paul A. Lopata, Thomas B. Bahder A general sensor can be modeled in the following way: a well-characterized physical system is prepared in some initial state, the system then interacts with a classical field through a well-understood mechanism, and then a measurement is made on the original system. From this procedure it is possible to infer the characteristics of the classical field. A number of proposals have been made to develop \textit{quantum sensors}, whose physical systems (which are prepared, interact with the classical field, and are then measured) are quantum mechanical in nature. In this talk I introduce this general description of quantum sensors and demonstrate how the unitary (interacting) dynamics and probabilistic measurements afforded by quantum mechanics can be used to infer the value of a classical field using a Bayesian statistical analysis. I also discuss the use of the mathematical measure of mutual information to compare different sensors. [Preview Abstract] |
Monday, March 5, 2007 8:48AM - 9:00AM |
A33.00003: Using a qubit to measure photon number statistics of a driven, thermal oscillator Aashish Clerk, Dian Wahyu Utami We demonstrate theoretically how photon number statistics of a driven, damped oscillator at finite temperature can be extracted by measuring the dephasing spectrum of a two-level system dispersively coupled to the oscillator; previous results only dealt with the purely thermal or zero-temperature driven cases [1][2]. We also consider the fidelity of this scheme-- to what extent does the measurement reflect the initial number statistics of the mode? Finally, we make a connection to the theory of full counting statistics in mesoscopic physics. Our results have relevance both to experiments in circuit cavity QED, as well as with quantum nano-electromechanical systems. \newline \newline [1] M.I. Dykman and M.A. Krivoglaz, Sov. Phys. Solid State 29, 210, (1987). \newline [2] J. Gambetta et al, Phys. Rev. A 74, 042318 (2006). [Preview Abstract] |
Monday, March 5, 2007 9:00AM - 9:12AM |
A33.00004: Evidence of Dispersive Coupling between a Nanomechanical Resonator and a Cooper-Pair Box Matthew LaHaye, Junho Suh, Pierre Echternach, Keith Schwab, Michael Roukes Many proposals have been put forth to prepare and observe quantum nano-electromechanical systems (quantum NEMS or QEMS) via coupling to a Cooper-pair box (CPB). A natural first step in the realization of these proposals is to study the dispersive interaction between a NEMS and CPB. In the dispersive limit, the coupling between the NEMS and CPB is a second-order effect that should result in a CPB-state-dependent renormalization of the nanoresonator's frequency. For typical parameters, the relative magnitude of the frequency shift should be a few ppm, resolvable with current NEMS detection capabilities. In fact, using a capacitive nanomechanical transduction scheme, we have been able to observe a red-shift of approximately 150 Hz in the frequency of a 61 MHz silicon nitride nanoresonator while tuning the ground state of a nearby CPB through a charge-degeneracy point. In my talk, I will present our most recent data and discuss the implications for the development of QEMS. [Preview Abstract] |
Monday, March 5, 2007 9:12AM - 9:24AM |
A33.00005: Laser cooling of a microcantilever using a medium-finesse optical cavity. Andrew Jayich, Benjamin Zwickl, Jack Harris We report on a Fabry-Perot optical cavity formed between a 30 $\mu $m-wide metal-coated microcantilever and a commercial concave dielectric mirror. A finesse of 55 is achieved with the mirrors 75 mm apart in a near-hemispherical geometry. This finesse was limited by loss in the metal coating of the cantilever; diffraction loss from the microcantilever was negligible. The cantilever was passively laser cooled from 300 K to 50 K when the cavity was detuned. [Preview Abstract] |
Monday, March 5, 2007 9:24AM - 9:36AM |
A33.00006: Noise Temperature and Thermodynamic Temperature of a Sample-on-Cantilever System Below 1K Ania Bleszynski, Will Shanks, Jack Harris Micromechanical systems such as cantilevers are frequently used to detect ultra-small forces and displacements. In a sample-on-cantilever geometry, operation at low temperature requires cooling the thermodynamic temperature of the sample T$_{S}$ and the noise temperature of the cantilever T$_{N}$. This can be challenging because for high-Q cantilevers, these temperatures are only weakly coupled. In addition, for insulating cantilevers monitored by a reflected laser beam, these temperatures may also be weakly coupled to the refrigerator temperature. We have made quantitative measurements of T$_{N}$ and T$_{S}$ for a sample-on-cantilever set-up as a function of incident laser power and refrigerator temperature below 1 Kelvin. We infer T$_{S}$ from measurements of the critical magnetic field of a superconducting sample mounted on the cantilever. T$_{N}$ is inferred from the cantilever's Brownian motion. We find that for this system both T$_{S}$ and T$_{N}$ remain quite close to the refrigerator temperature. [Preview Abstract] |
Monday, March 5, 2007 9:36AM - 9:48AM |
A33.00007: Intrinsic Noise Properties of Atomic Point Contact Displacement Detectors N. E. Flowers-Jacobs, K. W. Lehnert By coupling an atomic point contact (APC) to a nanomechanical beam, we measure the noise properties of an APC, an object which is the basis of scanning tunneling microscopy and is used to create electrical contact to single molecules. Using a microwave technique, we detect the resonant motion of the nanomechanical beam at frequencies up to 200 MHz. This measurement is sensitive enough to observe the random thermal motion of the nanomechanical beam at 250 mK. We use this thermal motion to evaluate the noise properties of the APC, demonstrating a displacement imprecision limited by the shot-noise in the number of electrons that tunnel across the APC and observing the force due to measurement backaction. Together, the imprecision and backaction yield a total uncertainty in the beam's displacement that is 42 times the standard quantum limit. In addition, we detect the beam's response to piezoelectric, electric, and magnetic forces, and use feedback to ``squash'' the shot-noise. [Preview Abstract] |
Monday, March 5, 2007 9:48AM - 10:00AM |
A33.00008: Heisenberg limited Sagnac interferometry Aziz Kolkiran, G.S. Agarwal When two electromagnetic waves counter-propagate along a circular path in rotation they experience different travel times to complete the path. This induces a phase shift between the two counter-propagating waves proportional to the angular velocity of the rotation. It was studied and used in optics only with lasers until recently when single photons were used. However, it turns out that the results of interference are no different than with classical sources. Thus a natural question would be --what is the nature of interference if we replace the single photon source by entangled photon pair source. This is what we examine in detail. We find that the sensitivity of Sagnac interferometer could be considerably improved by using entangled photons produced by a down-converter. We present analytic results for the sensitivity of the interferometer. In particular, two-photon and four-photon entanglements increase the sensitivity by a factor of 2 and 4 respectively. [Preview Abstract] |
Monday, March 5, 2007 10:00AM - 10:12AM |
A33.00009: Generalized Limits for Single-Parameter Quantum Estimation Sergio Boixo, Steven Flammia, J.M. Geremia, Carlton Caves We develop generalized bounds for quantum single-parameter estimation problems for which the coupling to the parameter is described by intrinsic multi-system interactions. For a Hamiltonian with $k$-system parameter-sensitive terms, the quantum limit scales as $1/N^k$ where $N$ is the number of systems. These quantum limits remain valid when the Hamiltonian is augmented by any parameter-independent interaction among the systems and when adaptive measurements via parameter-independent coupling to ancillas are allowed. [Preview Abstract] |
Monday, March 5, 2007 10:12AM - 10:24AM |
A33.00010: Quantum projection noise limited spectroscopy with ions in a Penning-Malmberg trap. ---Progress toward spin squeezed states. Nobuyasu Shiga, Wayne Itano, John Bollinger We describe plans and summarize initial progress towards making spin squeezed states with up to $\sim$100 $^{9}$Be$^{+}$ ions in a Penning-Malmberg trap. We use the ground-state electron spin-flip transition, which in the 4.5 T magnetic field of the trap has a transition frequency of 124 GHz, as the ion qubit. With a 30 mW Gunn diode oscillator we have observed Rabi flopping rates as high as $\sim$7 kHz. We will summarize experimental progress on realizing projection noise limited spectroscopy on this transition, which is a prerequisite for demonstrating spin squeezing. For entangling the ions we plan to use a generalization of the few ion qubit phase gate developed at NIST \footnote{D. Leibfried, et al., Nature {\bf 438}, 639 (2005).} to generate an $\exp{(i\chi {J_{z}}^2 t)}$ interaction between all of the ion qubits. This interaction can be implemented on a single plane of ions \footnote{T.B. Mitchell, et al., Science {\bf 282}, 1290 (1998).} with a motional sideband, stimulated Raman transition. [Preview Abstract] |
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