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Papers by Pen-Li Yu
Solid State Communications, 2009
We investigate the scenario of competing order (CO) induced Fermi arcs and pseudogap in cuprate s... more We investigate the scenario of competing order (CO) induced Fermi arcs and pseudogap in cuprate superconductors. For hole-type cuprates, both phenomena as a function of temperature and doping level can be accounted for if the CO vanishes at T* above the superconducting transition T c and the CO wave-vector Q is parallel to the antinodal direction. In contrast, the absence of these phenomena and the non-monotonic d-wave gap in electron-type cuprates may be attributed to T* < T c and a CO wave-vector Q parallel to the nodal direction.
Conference on Lasers and Electro-Optics 2012, 2012
ABSTRACT We have constructed a monolithic Fabry-Perot cavity optomechanical system. From cryogeni... more ABSTRACT We have constructed a monolithic Fabry-Perot cavity optomechanical system. From cryogenic temperatures we significantly damp a Si3N4-membrane and achieve conditions suitable for cooling MHz mechanical resonators from ~ 4 K into the quantum regime.
CLEO: 2013, 2013
We study methods to improve the Q of a variety of highly-stressed resonators for cavity optomecha... more We study methods to improve the Q of a variety of highly-stressed resonators for cavity optomechanics. We realize ultrahigh-Q metal/Si 3 N 4 membranes and crystalline membranes, and have begun to control external dissipation via modified support structures.
The radiation pressure of light can act to damp and cool the vibrational motion of a mechanical r... more The radiation pressure of light can act to damp and cool the vibrational motion of a mechanical resonator, but even if the light field has no thermal component, shot noise still sets a limit on the minimum phonon occupation. In optomechanical sideband cooling in a cavity, the finite off-resonant Stokes scattering defined by the cavity linewidth combined with shot noise fluctuations dictates a quantum backaction limit, analogous to the Doppler limit of atomic laser cooling. In our work, we sideband cool a micromechanical membrane resonator to the quantum backaction limit. Monitoring the optical sidebands allows us to directly observe the mechanical object come to thermal equilibrium with the optical bath. This level of optomechanical coupling that overwhelms the intrinsic thermal decoherence was not reached in previous ground-state cooling demonstrations.
We investigate the optomechanical properties of tensile-strained ternary InGaP nanomembranes grow... more We investigate the optomechanical properties of tensile-strained ternary InGaP nanomembranes grown on GaAs. This material system combines the benefits of highly strained membranes, similar to those based on stoichiometric silicon nitride, with the unique properties of thin-film semiconductor single crystals, as previously demonstrated with suspended GaAs. Here, we employ lattice mismatch in epitaxial growth to impart an intrinsic tensile strain to a monocrystalline thin film (approximately 30nm thick). These structures exhibit mechanical quality factors of 2?106 or beyond at room temperature and 17K for eigenfrequencies up to 1MHz, yielding Qxfproducts of 2?1012Hz for a tensile stress of ~170MPa. Incorporating such membranes in a high-finesse Fabry-Perot cavity, we extract an upper limit to the total optical loss (including both absorption and scatter) of 40 ppm at 1064nm and room temperature. Further reductions of the In content of this alloy will enable tensile stress levels of 1GPa, with the potential for a significant increase in the Qxf product, assuming no deterioration in the mechanical loss at this composition and strain level. This materials system is a promising candidate for the integration of strained semiconductor membrane structures with low-loss semiconductor mirrors and for realizing stacks of membranes for enhanced optomechanical coupling.
We describe a cryogenic cavity-optomechanical system that combines Si3N4 membranes with a mechani... more We describe a cryogenic cavity-optomechanical system that combines Si3N4 membranes with a mechanically rigid Fabry–Perot cavity. The extremely high products of quality factor and frequency of the membranes allow us to cool a MHz mechanical mode to a phonon occupation of n <10, starting at a bath temperature of 5 K.We show that even at cold temperatures thermally occupied mechanical modes of the cavity elements can be a limitation, and we discuss methods to reduce these effects sufficiently for achieving ground state cooling. This promising new platform should have versatile uses for hybrid devices and searches for radiation pressure shot noise.
The temperature dependence of the asymmetry between Stokes and anti-Stokes Raman scattering can b... more The temperature dependence of the asymmetry between Stokes and anti-Stokes Raman scattering can be exploited for self-calibrating, optically based thermometry. In the context of cavity optomechanics, we observe the cavity-enhanced scattering of light interacting with the standing-wave drumhead modes of a Si3N4 membrane mechanical resonator. The ratio of the amplitude of Stokes to anti-Stokes scattered light is used to measure temperatures of optically cooled mechanical modes, down to the level of a few vibrational quanta. We demonstrate that the Raman-ratio technique allows the measurement of the physical temperature of our device over a range extending from cryogenic temperatures to within an order of magnitude of room temperature.
A phononic crystal can control the acoustic coupling between a resonator and its support structur... more A phononic crystal can control the acoustic coupling between a resonator and its support structure. We micromachine a phononic bandgap shield for high Q silicon nitride membranes and study the driven displacement spectra of the membranes and their support structures. We find that inside the observed bandgaps, the density and amplitude of non-membrane modes are greatly suppressed, and membrane modes are shielded from an external mechanical drive by up to 30 dB. V C 2014 AIP Publishing LLC. [http://dx.
We study the mechanical quality factors of bilayer aluminum/silicon-nitride membranes. By coating... more We study the mechanical quality factors of bilayer aluminum/silicon-nitride membranes. By coating ultrahigh-Q Si3N4 membranes with a more lossy metal, we can precisely measure the effect of material loss on Q's of tensioned resonator modes over a large range of frequencies. We develop a theoretical model that interprets our results and predicts the damping can be reduced significantly by patterning the metal film. Using such patterning, we fabricate Al-Si3N4 membranes with ultrahigh Q at room temperature. Our work elucidates the role of material loss in the Q of membrane resonators and informs the design of hybrid mechanical oscillators for optical-electrical-mechanical quantum interfaces.
Interferometry is a ubiquitous method for sensitive displacement measurements. In typical inter-f... more Interferometry is a ubiquitous method for sensitive displacement measurements. In typical inter-ferometry employing a coherent state, the amplitude and phase quantum fluctuations are both at the shot noise level. Recently optomechanical systems have been developed that not only measure mechanical motion, but can also manipulate the motion with radiation pressure. For example, radiation forces have been used to cool mechanical resonators to near their quantum ground state [1, 2]. With sufficiently strong radiation pressure, quantum fluctuations can become the dominant mechanical driving force, leading to correlations between the mechanical motion and the quantum fluctuations of the optical field [4]. Such correlations can be used to suppress fluctuations on an interferometer's output optical field below the shot noise level [2, 3], at the expense of increasing fluctuations in an orthogonal quadrature. This method of manipulating the quantum fluctuations is termed ponderomotive [6] squeezing. Here, we observe ponderomotive squeezing at 1.7±0.2 dB below (32% below) the shot noise level and optical amplification of quantum fluctuations by over 25 dB. The squeezing is realized on light transmitted through a Fabry-Perot interferometer with an embedded mechanically compliant dielectric membrane.
Thesis Chapters by Pen-Li Yu
Mechanical oscillators coupled to an electromagnetic cavity have emerged as a new frontier in qua... more Mechanical oscillators coupled to an electromagnetic cavity have emerged as a new frontier in quantum optics. This coupling presents an opportunity for manipulating the quantum state of light, connecting different quantum resources, and ultra-sensitive force detectors. A particular enabling platform utilizes high-stress silicon-nitride membrane resonators. Because of its large tensile stress, the membrane exhibits remarkable mechanical quality factors (Qs) that are even higher than that of single crystalline silicon. The membrane with such high Q combined with robust cryogenic Fabry-Perot cavity enables a variety of quantum optics experiments, such as squeezed light generation. Improving upon these encouraging results requires understanding and engineering the membrane resonators. The membrane dissipation can be classified as the internal loss and the external loss. We are able to manage the internal loss of a hybrid membrane with a curvature map, and control the external loss of a membrane with a phononic crystal (PnC) shield. In this dissertation, I will present our studies and engineering of high-stress membrane mechanics, squeezed light generation, and optomechanical Raman-ratio thermometry with a PnC-isolated membrane.
Solid State Communications, 2009
We investigate the scenario of competing order (CO) induced Fermi arcs and pseudogap in cuprate s... more We investigate the scenario of competing order (CO) induced Fermi arcs and pseudogap in cuprate superconductors. For hole-type cuprates, both phenomena as a function of temperature and doping level can be accounted for if the CO vanishes at T* above the superconducting transition T c and the CO wave-vector Q is parallel to the antinodal direction. In contrast, the absence of these phenomena and the non-monotonic d-wave gap in electron-type cuprates may be attributed to T* < T c and a CO wave-vector Q parallel to the nodal direction.
Conference on Lasers and Electro-Optics 2012, 2012
ABSTRACT We have constructed a monolithic Fabry-Perot cavity optomechanical system. From cryogeni... more ABSTRACT We have constructed a monolithic Fabry-Perot cavity optomechanical system. From cryogenic temperatures we significantly damp a Si3N4-membrane and achieve conditions suitable for cooling MHz mechanical resonators from ~ 4 K into the quantum regime.
CLEO: 2013, 2013
We study methods to improve the Q of a variety of highly-stressed resonators for cavity optomecha... more We study methods to improve the Q of a variety of highly-stressed resonators for cavity optomechanics. We realize ultrahigh-Q metal/Si 3 N 4 membranes and crystalline membranes, and have begun to control external dissipation via modified support structures.
The radiation pressure of light can act to damp and cool the vibrational motion of a mechanical r... more The radiation pressure of light can act to damp and cool the vibrational motion of a mechanical resonator, but even if the light field has no thermal component, shot noise still sets a limit on the minimum phonon occupation. In optomechanical sideband cooling in a cavity, the finite off-resonant Stokes scattering defined by the cavity linewidth combined with shot noise fluctuations dictates a quantum backaction limit, analogous to the Doppler limit of atomic laser cooling. In our work, we sideband cool a micromechanical membrane resonator to the quantum backaction limit. Monitoring the optical sidebands allows us to directly observe the mechanical object come to thermal equilibrium with the optical bath. This level of optomechanical coupling that overwhelms the intrinsic thermal decoherence was not reached in previous ground-state cooling demonstrations.
We investigate the optomechanical properties of tensile-strained ternary InGaP nanomembranes grow... more We investigate the optomechanical properties of tensile-strained ternary InGaP nanomembranes grown on GaAs. This material system combines the benefits of highly strained membranes, similar to those based on stoichiometric silicon nitride, with the unique properties of thin-film semiconductor single crystals, as previously demonstrated with suspended GaAs. Here, we employ lattice mismatch in epitaxial growth to impart an intrinsic tensile strain to a monocrystalline thin film (approximately 30nm thick). These structures exhibit mechanical quality factors of 2?106 or beyond at room temperature and 17K for eigenfrequencies up to 1MHz, yielding Qxfproducts of 2?1012Hz for a tensile stress of ~170MPa. Incorporating such membranes in a high-finesse Fabry-Perot cavity, we extract an upper limit to the total optical loss (including both absorption and scatter) of 40 ppm at 1064nm and room temperature. Further reductions of the In content of this alloy will enable tensile stress levels of 1GPa, with the potential for a significant increase in the Qxf product, assuming no deterioration in the mechanical loss at this composition and strain level. This materials system is a promising candidate for the integration of strained semiconductor membrane structures with low-loss semiconductor mirrors and for realizing stacks of membranes for enhanced optomechanical coupling.
We describe a cryogenic cavity-optomechanical system that combines Si3N4 membranes with a mechani... more We describe a cryogenic cavity-optomechanical system that combines Si3N4 membranes with a mechanically rigid Fabry–Perot cavity. The extremely high products of quality factor and frequency of the membranes allow us to cool a MHz mechanical mode to a phonon occupation of n <10, starting at a bath temperature of 5 K.We show that even at cold temperatures thermally occupied mechanical modes of the cavity elements can be a limitation, and we discuss methods to reduce these effects sufficiently for achieving ground state cooling. This promising new platform should have versatile uses for hybrid devices and searches for radiation pressure shot noise.
The temperature dependence of the asymmetry between Stokes and anti-Stokes Raman scattering can b... more The temperature dependence of the asymmetry between Stokes and anti-Stokes Raman scattering can be exploited for self-calibrating, optically based thermometry. In the context of cavity optomechanics, we observe the cavity-enhanced scattering of light interacting with the standing-wave drumhead modes of a Si3N4 membrane mechanical resonator. The ratio of the amplitude of Stokes to anti-Stokes scattered light is used to measure temperatures of optically cooled mechanical modes, down to the level of a few vibrational quanta. We demonstrate that the Raman-ratio technique allows the measurement of the physical temperature of our device over a range extending from cryogenic temperatures to within an order of magnitude of room temperature.
A phononic crystal can control the acoustic coupling between a resonator and its support structur... more A phononic crystal can control the acoustic coupling between a resonator and its support structure. We micromachine a phononic bandgap shield for high Q silicon nitride membranes and study the driven displacement spectra of the membranes and their support structures. We find that inside the observed bandgaps, the density and amplitude of non-membrane modes are greatly suppressed, and membrane modes are shielded from an external mechanical drive by up to 30 dB. V C 2014 AIP Publishing LLC. [http://dx.
We study the mechanical quality factors of bilayer aluminum/silicon-nitride membranes. By coating... more We study the mechanical quality factors of bilayer aluminum/silicon-nitride membranes. By coating ultrahigh-Q Si3N4 membranes with a more lossy metal, we can precisely measure the effect of material loss on Q's of tensioned resonator modes over a large range of frequencies. We develop a theoretical model that interprets our results and predicts the damping can be reduced significantly by patterning the metal film. Using such patterning, we fabricate Al-Si3N4 membranes with ultrahigh Q at room temperature. Our work elucidates the role of material loss in the Q of membrane resonators and informs the design of hybrid mechanical oscillators for optical-electrical-mechanical quantum interfaces.
Interferometry is a ubiquitous method for sensitive displacement measurements. In typical inter-f... more Interferometry is a ubiquitous method for sensitive displacement measurements. In typical inter-ferometry employing a coherent state, the amplitude and phase quantum fluctuations are both at the shot noise level. Recently optomechanical systems have been developed that not only measure mechanical motion, but can also manipulate the motion with radiation pressure. For example, radiation forces have been used to cool mechanical resonators to near their quantum ground state [1, 2]. With sufficiently strong radiation pressure, quantum fluctuations can become the dominant mechanical driving force, leading to correlations between the mechanical motion and the quantum fluctuations of the optical field [4]. Such correlations can be used to suppress fluctuations on an interferometer's output optical field below the shot noise level [2, 3], at the expense of increasing fluctuations in an orthogonal quadrature. This method of manipulating the quantum fluctuations is termed ponderomotive [6] squeezing. Here, we observe ponderomotive squeezing at 1.7±0.2 dB below (32% below) the shot noise level and optical amplification of quantum fluctuations by over 25 dB. The squeezing is realized on light transmitted through a Fabry-Perot interferometer with an embedded mechanically compliant dielectric membrane.
Mechanical oscillators coupled to an electromagnetic cavity have emerged as a new frontier in qua... more Mechanical oscillators coupled to an electromagnetic cavity have emerged as a new frontier in quantum optics. This coupling presents an opportunity for manipulating the quantum state of light, connecting different quantum resources, and ultra-sensitive force detectors. A particular enabling platform utilizes high-stress silicon-nitride membrane resonators. Because of its large tensile stress, the membrane exhibits remarkable mechanical quality factors (Qs) that are even higher than that of single crystalline silicon. The membrane with such high Q combined with robust cryogenic Fabry-Perot cavity enables a variety of quantum optics experiments, such as squeezed light generation. Improving upon these encouraging results requires understanding and engineering the membrane resonators. The membrane dissipation can be classified as the internal loss and the external loss. We are able to manage the internal loss of a hybrid membrane with a curvature map, and control the external loss of a membrane with a phononic crystal (PnC) shield. In this dissertation, I will present our studies and engineering of high-stress membrane mechanics, squeezed light generation, and optomechanical Raman-ratio thermometry with a PnC-isolated membrane.