alex krause - Academia.edu (original) (raw)

Papers by alex krause

Research paper thumbnail of Subject Areas: Atomic and Molecular Physics, Quantum Physics A Viewpoint on: Observation of Quantum Motion of a Nanomechanical Resonator

A technique from ion spectroscopy reveals the quantum nature of a mechanical system at low tem-pe... more A technique from ion spectroscopy reveals the quantum nature of a mechanical system at low tem-perature.

Research paper thumbnail of Feasability of Measuring Radiation Pressure Quantum Back-Action in Zipper Photonic Crystal Optomechanical Cavities

Conference on Lasers and Electro-Optics 2010, 2010

Treatment of crop residues with some species of white-rot fungi can enhance the nutritive value. ... more Treatment of crop residues with some species of white-rot fungi can enhance the nutritive value. After the fungal treatment of sorghum (Sorghum bicolor) stover with two white-rot fungi in a solid state fermentation, the chemical composition and in vitro digestibility of the resultant substrate was determined. The results show a significant (p < 0.05) increase in crude protein contents from 2.54% for the control to 4.51% for Pleurotus ostreatus (POS) and 4.59% for Pleurotus sajor pulmonarius (PPT). The nitrogen free extract (NFE) content also increased significantly (p < 0.05). The crude fibre decreased significantly from 31.65% for the control to 27.49% for POS and 23.54% for PPS. There were also consistent significant decreases (p < 0.05) in the values obtained for NDF, ADF ADL. Significant differences were also observed in the hemicellulose and cellulose contents. Fermentation of the insoluble fraction (b) was enhanced by the fungal treatment. Wide variations were also observed in the mineral contents of the different substrates The estimated organic matter digestibility (OMD) ranged from 42.99 to 57.75%, short chain fatty acid ranged from 0.56 to 0.94 µM and metabolisable energy (ME) ranged from 5.97 to 8.21 MJ/Kg DM. This result suggests that fungal treatment of sorghum stover resulted in improved CP and digestibility, hence its potential in ruminant nutrition.

Research paper thumbnail of Observation of Quantum Motion of a Nanomechanical Resonator

Physical Review Letters, 2012

In this work we use resolved sideband laser cooling to cool a mesoscopic mechanical resonator to ... more In this work we use resolved sideband laser cooling to cool a mesoscopic mechanical resonator to near its quantum ground state (phonon occupancy 2.6 ± 0.2), and observe the motional sidebands generated on a second probe laser. Asymmetry in the sideband amplitudes provides a direct measure of the displacement noise power associated with quantum zero-point fluctuations of the nanomechanical resonator, and allows for an intrinsic calibration of the phonon occupation number.

Research paper thumbnail of Laser cooling of a nanomechanical oscillator into its quantum ground state

Nature, 2011

A patterned Si nanobeam is formed which supports co-localized acoustic and optical resonances tha... more A patterned Si nanobeam is formed which supports co-localized acoustic and optical resonances that are coupled via radiation pressure. Starting from a bath temperature of T b ≈ 20 K, the 3.68 GHz nanomechanical mode is cooled into its quantum mechanical ground state utilizing optical radiation pressure. The mechanical mode displacement fluctuations, imprinted on the transmitted cooling laser beam, indicate that a final phonon mode occupancy ofn = 0.85 ± 0.04 is obtained.

Research paper thumbnail of Laser cooling of a nanomechanical oscillator into its quantum ground state

Nature, 2011

A patterned Si nanobeam is formed which supports co-localized acoustic and optical resonances tha... more A patterned Si nanobeam is formed which supports co-localized acoustic and optical resonances that are coupled via radiation pressure. Starting from a bath temperature of T b ≈ 20 K, the 3.68 GHz nanomechanical mode is cooled into its quantum mechanical ground state utilizing optical radiation pressure. The mechanical mode displacement fluctuations, imprinted on the transmitted cooling laser beam, indicate that a final phonon mode occupancy ofn = 0.85 ± 0.04 is obtained.

Research paper thumbnail of Optical read out and feedback cooling of a nanostring optomechanical cavity

Optical measurement of the motion of a 940 kHz mechanical resonance of a silicon nitride nanostri... more Optical measurement of the motion of a 940 kHz mechanical resonance of a silicon nitride nanostring resonator is demonstrated with a read out noise imprecision reaching 37 dB below that of the resonator's zero-point fluctuations. Via intensity modulation of the optical probe laser, radiation pressure feedback is used to cool and damp the mechanical mode from an initial room temperature occupancy of n̅_b = 6.5 × 10^6 (T_b=295K) down to a phonon occupation of 〈 n 〉 = 66 ± 10, representing a mode temperature of T_m≈ 3mK. The five decades of cooling is enabled by the system's large single-photon cooperativity (C_1 = 4) and high quantum efficiency of optical motion detection (η_t = 0.27).

Research paper thumbnail of Optical read out and feedback cooling of a nanostring optomechanical cavity

arXiv: Optics, 2015

Optical measurement of the motion of a 940 kHz mechanical resonance of a silicon nitride nanostri... more Optical measurement of the motion of a 940 kHz mechanical resonance of a silicon nitride nanostring resonator is demonstrated with a read out noise imprecision reaching 37 dB below that of the resonator's zero-point fluctuations. Via intensity modulation of the optical probe laser, radiation pressure feedback is used to cool and damp the mechanical mode from an initial room temperature occupancy of n_b=6.5×10^6 (T_b=295K) down to a phonon occupation of (n)=66±10, representing a mode temperature of T_m≈3mK. The five decades of cooling is enabled by the system's large single-photon cooperativity (C_1=4) and high quantum efficiency of optical motion detection (η_t=0.27).

Research paper thumbnail of Chip-Scale Cavity-Optomechanical Accelerometer

ABSTRACT We demonstrate an optomechanical accelerometer using a v-groove fiber coupled photonic c... more ABSTRACT We demonstrate an optomechanical accelerometer using a v-groove fiber coupled photonic crystal nanocavity integrated with a high-Q nanotethered test mass. The nanocavity frequency can be tuned to that of an input laser by on-chip capacitive actuators.

Research paper thumbnail of Nonlinear radiation pressure dynamics in an optomechanical crystal

Utilizing a silicon nanobeam optomechanical crystal, we investigate the attractor diagram arising... more Utilizing a silicon nanobeam optomechanical crystal, we investigate the attractor diagram arising from the radiation pressure interaction between a localized optical cavity at lambda=1552\lambda = 1552lambda=1552nm and a mechanical resonance at omega/2pi=3.72\omega/2\pi = 3.72omega/2pi=3.72GHz. At a temperature of Tapprox10T \approx 10Tapprox10K, highly nonlinear driving of mechanical motion is observed via continuous wave optical pumping. Introduction of a time-dependent (modulated) optical pump is used to steer the system towards an otherwise inaccessible dynamically stable attractor in which mechanical self-oscillation occurs for an optical pump red-detuned from the cavity resonance. An analytical model incorporating thermo-optic effects due to optical absorption heating is developed, and found to accurately predict the measured device behavior.

Research paper thumbnail of Subject Areas: Atomic and Molecular Physics, Quantum Physics A Viewpoint on: Observation of Quantum Motion of a Nanomechanical Resonator

A technique from ion spectroscopy reveals the quantum nature of a mechanical system at low tem-pe... more A technique from ion spectroscopy reveals the quantum nature of a mechanical system at low tem-perature.

Research paper thumbnail of Feasability of Measuring Radiation Pressure Quantum Back-Action in Zipper Photonic Crystal Optomechanical Cavities

Conference on Lasers and Electro-Optics 2010, 2010

Treatment of crop residues with some species of white-rot fungi can enhance the nutritive value. ... more Treatment of crop residues with some species of white-rot fungi can enhance the nutritive value. After the fungal treatment of sorghum (Sorghum bicolor) stover with two white-rot fungi in a solid state fermentation, the chemical composition and in vitro digestibility of the resultant substrate was determined. The results show a significant (p < 0.05) increase in crude protein contents from 2.54% for the control to 4.51% for Pleurotus ostreatus (POS) and 4.59% for Pleurotus sajor pulmonarius (PPT). The nitrogen free extract (NFE) content also increased significantly (p < 0.05). The crude fibre decreased significantly from 31.65% for the control to 27.49% for POS and 23.54% for PPS. There were also consistent significant decreases (p < 0.05) in the values obtained for NDF, ADF ADL. Significant differences were also observed in the hemicellulose and cellulose contents. Fermentation of the insoluble fraction (b) was enhanced by the fungal treatment. Wide variations were also observed in the mineral contents of the different substrates The estimated organic matter digestibility (OMD) ranged from 42.99 to 57.75%, short chain fatty acid ranged from 0.56 to 0.94 µM and metabolisable energy (ME) ranged from 5.97 to 8.21 MJ/Kg DM. This result suggests that fungal treatment of sorghum stover resulted in improved CP and digestibility, hence its potential in ruminant nutrition.

Research paper thumbnail of Observation of Quantum Motion of a Nanomechanical Resonator

Physical Review Letters, 2012

In this work we use resolved sideband laser cooling to cool a mesoscopic mechanical resonator to ... more In this work we use resolved sideband laser cooling to cool a mesoscopic mechanical resonator to near its quantum ground state (phonon occupancy 2.6 ± 0.2), and observe the motional sidebands generated on a second probe laser. Asymmetry in the sideband amplitudes provides a direct measure of the displacement noise power associated with quantum zero-point fluctuations of the nanomechanical resonator, and allows for an intrinsic calibration of the phonon occupation number.

Research paper thumbnail of Laser cooling of a nanomechanical oscillator into its quantum ground state

Nature, 2011

A patterned Si nanobeam is formed which supports co-localized acoustic and optical resonances tha... more A patterned Si nanobeam is formed which supports co-localized acoustic and optical resonances that are coupled via radiation pressure. Starting from a bath temperature of T b ≈ 20 K, the 3.68 GHz nanomechanical mode is cooled into its quantum mechanical ground state utilizing optical radiation pressure. The mechanical mode displacement fluctuations, imprinted on the transmitted cooling laser beam, indicate that a final phonon mode occupancy ofn = 0.85 ± 0.04 is obtained.

Research paper thumbnail of Laser cooling of a nanomechanical oscillator into its quantum ground state

Nature, 2011

A patterned Si nanobeam is formed which supports co-localized acoustic and optical resonances tha... more A patterned Si nanobeam is formed which supports co-localized acoustic and optical resonances that are coupled via radiation pressure. Starting from a bath temperature of T b ≈ 20 K, the 3.68 GHz nanomechanical mode is cooled into its quantum mechanical ground state utilizing optical radiation pressure. The mechanical mode displacement fluctuations, imprinted on the transmitted cooling laser beam, indicate that a final phonon mode occupancy ofn = 0.85 ± 0.04 is obtained.

Research paper thumbnail of Optical read out and feedback cooling of a nanostring optomechanical cavity

Optical measurement of the motion of a 940 kHz mechanical resonance of a silicon nitride nanostri... more Optical measurement of the motion of a 940 kHz mechanical resonance of a silicon nitride nanostring resonator is demonstrated with a read out noise imprecision reaching 37 dB below that of the resonator's zero-point fluctuations. Via intensity modulation of the optical probe laser, radiation pressure feedback is used to cool and damp the mechanical mode from an initial room temperature occupancy of n̅_b = 6.5 × 10^6 (T_b=295K) down to a phonon occupation of 〈 n 〉 = 66 ± 10, representing a mode temperature of T_m≈ 3mK. The five decades of cooling is enabled by the system's large single-photon cooperativity (C_1 = 4) and high quantum efficiency of optical motion detection (η_t = 0.27).

Research paper thumbnail of Optical read out and feedback cooling of a nanostring optomechanical cavity

arXiv: Optics, 2015

Optical measurement of the motion of a 940 kHz mechanical resonance of a silicon nitride nanostri... more Optical measurement of the motion of a 940 kHz mechanical resonance of a silicon nitride nanostring resonator is demonstrated with a read out noise imprecision reaching 37 dB below that of the resonator's zero-point fluctuations. Via intensity modulation of the optical probe laser, radiation pressure feedback is used to cool and damp the mechanical mode from an initial room temperature occupancy of n_b=6.5×10^6 (T_b=295K) down to a phonon occupation of (n)=66±10, representing a mode temperature of T_m≈3mK. The five decades of cooling is enabled by the system's large single-photon cooperativity (C_1=4) and high quantum efficiency of optical motion detection (η_t=0.27).

Research paper thumbnail of Chip-Scale Cavity-Optomechanical Accelerometer

ABSTRACT We demonstrate an optomechanical accelerometer using a v-groove fiber coupled photonic c... more ABSTRACT We demonstrate an optomechanical accelerometer using a v-groove fiber coupled photonic crystal nanocavity integrated with a high-Q nanotethered test mass. The nanocavity frequency can be tuned to that of an input laser by on-chip capacitive actuators.

Research paper thumbnail of Nonlinear radiation pressure dynamics in an optomechanical crystal

Utilizing a silicon nanobeam optomechanical crystal, we investigate the attractor diagram arising... more Utilizing a silicon nanobeam optomechanical crystal, we investigate the attractor diagram arising from the radiation pressure interaction between a localized optical cavity at lambda=1552\lambda = 1552lambda=1552nm and a mechanical resonance at omega/2pi=3.72\omega/2\pi = 3.72omega/2pi=3.72GHz. At a temperature of Tapprox10T \approx 10Tapprox10K, highly nonlinear driving of mechanical motion is observed via continuous wave optical pumping. Introduction of a time-dependent (modulated) optical pump is used to steer the system towards an otherwise inaccessible dynamically stable attractor in which mechanical self-oscillation occurs for an optical pump red-detuned from the cavity resonance. An analytical model incorporating thermo-optic effects due to optical absorption heating is developed, and found to accurately predict the measured device behavior.