In many experiments involving conversion of quantum degenerate atomic gases into molecular dimers... more In many experiments involving conversion of quantum degenerate atomic gases into molecular dimers via a Feshbach resonance, an external magnetic field is linearly swept from above the resonance to below resonance. In the adiabatic limit, the fraction of atoms converted into molecules is independent of the functional form of the sweep and is predicted to be 100%. However, for nonadiabatic sweeps through resonance, Landau-Zener theory predicts that a linear sweep will result in a negligible production of molecules. Here we employ a genetic algorithm to determine the functional time dependence of the magnetic field that produces the maximum number of molecules for sweep times that are comparable to the period of resonant atom-molecule oscillations, 2πΩ −1
We study the photo-association of Bose-Einstein condensed atoms into molecules using a quantized ... more We study the photo-association of Bose-Einstein condensed atoms into molecules using a quantized cavity field. The semiclassical stationary solutions for the three nonlinearly coupled bosonic fields are found and their stability and scaling properties in terms of physical parameters are determined. The full quantum dynamics are simulated using the positive-P distribution and a reduced dynamics in terms of molecule fraction and relative phase between atoms and molecules, which can be mapped onto a Bloch-sphere. Quantum effects at the cross over from stable steady state behavior to large amplitude nonlinear Rabi-oscillations as a function of particle number and inter-particle interaction strengths are investigated.
In many experiments involving conversion of quantum degenerate atomic gases into molecular dimers... more In many experiments involving conversion of quantum degenerate atomic gases into molecular dimers via a Feshbach resonance, an external magnetic field is linearly swept from above the resonance to below resonance. In the adiabatic limit, the fraction of atoms converted into molecules is independent of the functional form of the sweep and is predicted to be 100%. However, for nonadiabatic sweeps through resonance, Landau-Zener theory predicts that a linear sweep will result in a negligible production of molecules. Here we employ a genetic algorithm to determine the functional time dependence of the magnetic field that produces the maximum number of molecules for sweep times that are comparable to the period of resonant atom-molecule oscillations, 2πΩ −1
In many experiments involving conversion of quantum degenerate atomic gases into molecular dimers... more In many experiments involving conversion of quantum degenerate atomic gases into molecular dimers via a Feshbach resonance, an external magnetic field is linearly swept from above the resonance to below resonance. In the adiabatic limit, the fraction of atoms converted into molecules is independent of the functional form of the sweep and is predicted to be 100%. However, for nonadiabatic sweeps through resonance, Landau-Zener theory predicts that a linear sweep will result in a negligible production of molecules. Here we employ a genetic algorithm to determine the functional time dependence of the magnetic field that produces the maximum number of molecules for sweep times that are comparable to the period of resonant atom-molecule oscillations, 2πΩ −1
We examine a ballistic electron Aharonov-Bohm interferometer with a single dot embedded in each o... more We examine a ballistic electron Aharonov-Bohm interferometer with a single dot embedded in each of two arms that are connected in parallel to leads allowing the flow of current by sequential tunneling of electrons through the dots. We focus on the effect that correlations between dots due to the inter-dot spin-spin interactions have on the current-voltage(I-V) and frequency dependent current shot noise. The inter-dot spin-spin interaction is created by embedding the interferometer in an optical microcavity whose modes are far off-resonant with the intra-dot transitions and allows for a cavity mediated exchange of virtual photons between dots. With proper AB phase, inter-dot Coulomb repulsion, and inter-dot cavity mediated coupling, we can control the probability amplitudes for different tunneling paths of the interferometer and the probability of formation of inter-dot entangled spin triplet/singlet states. We analyze the dual effects of inter-dot cavity coupling and two-path interference on the I-V characteristics and shot noise correlations for charge and spin resolved currents in order to determine the conditions for optimal spin triplet/singlet state formation and how they are revealed in the current and noise. We also quantify the level of entanglement between the dots and investigate correlation of shot noise with entanglement measures.
The Sagnac effect is an important phase coherent effect in optical and atom interferometers where... more The Sagnac effect is an important phase coherent effect in optical and atom interferometers where rotations of the interferometer with respect to an inertial reference frame result in a shift in the interference pattern proportional to the rotation rate. Here we analyze for the first time the Sagnac effect in a mesoscopic semiconductor electron interferometer. We include in our analysis Rashba spin-orbit interactions in the ring. Our results indicate that spin-orbit interactions increase the rotation induced phase shift. We discuss the potential experimental observability of the Sagnac phase shift in such mesoscopic systems. PACS numbers: 73.23.-b, 03.75.-b, 72.25.Dc
Here we explore spin dependent quantum transport through a single quantum dot coupled to an optic... more Here we explore spin dependent quantum transport through a single quantum dot coupled to an optical microcavity. The spin current is generated by electron tunneling between a single doped reservoir and the dot combined with intradot spin flip transitions induced by a quantized cavity mode. In the limit of strong Coulomb blockade, this model is analogous to the Jaynes-Cummings model in quantum optics and generates a pure spin current in the absence of any charge current. Earlier research has shown that in the classical limit where a large number of such dots interact with the cavity field, the spin current exhibits bistability as a function of the laser amplitude that drives the cavity. We show that in the limit of a single quantum dot this bistability continues to be present in the intracavity photon statistics. Signatures of the bistable photon statistics manifest themselves in the frequency dependent shot noise of the spin current despite the fact that the quantum mechanical average spin current no longer exhibits bistability. Besides having significance for future quantum dot based optoelectronic devices, our results shed light on the relation between bistability, which is traditionally viewed as a classical effect, and quantum mechanics.
The Sagnac effect is an important phase coherent effect in optical and atom interferometers where... more The Sagnac effect is an important phase coherent effect in optical and atom interferometers where rotations of the interferometer with respect to an inertial reference frame result in a shift in the interference pattern proportional to the rotation rate. Here we analyze for the first time the Sagnac effect in a mesoscopic semiconductor electron interferometer. We include in our analysis Rashba spin-orbit interactions in the ring. Our results indicate that spin-orbit interactions increase the rotation induced phase shift. We discuss the potential experimental observability of the Sagnac phase shift in such mesoscopic systems. PACS numbers: 73.23.-b, 03.75.-b, 72.25.Dc
We examine the spin current and the associated shot noise generated in a quantum dot connected to... more We examine the spin current and the associated shot noise generated in a quantum dot connected to normal leads with zero bias voltage across the dot. The spin current is generated by spin flip transitions induced by a quantized electromagnetic field inside a cavity with one of the Zeeman states lying below the Fermi level of the leads and the other above. In the limit of strong Coulomb blockade, this model is analogous to the Jaynes-Cummings model in quantum optics. We also calculate the photon current and photon current shot noise resulting from photons leaking out of the cavity. We show that the photon current is equal to the spin current and that the spin current can be significantly larger than for the case of a classical driving field as a result of cavity losses. In addition to this, the frequency dependent spin (photon) current shot noise show dips (peaks) that are a result of the discrete nature of photons.
We examine an electron Aharonov-Bohm (AB) interferometer with individual quantum dots connected i... more We examine an electron Aharonov-Bohm (AB) interferometer with individual quantum dots connected in parallel to macroscopic leads. Here, we focus on the effect that both interdot spin-spin exchange interactions and intradot spin flips have on the current- and frequency-dependent current shot noise. By appropriate control of AB magnetic flux, interdot Coulomb repulsion, intradot spin flips, and interdot spin-spin coupling, the probability amplitudes for the different paths of the interferometer can be controlled, leading to broad tunability of both the shape and the contrast of interference fringes in the current. We also show that in the shot noise at finite frequencies corresponding to the spin-spin interaction energies, the noise shows a pronounced super-Poissonian and sub-Poissonian structure. AB flux, which is not an integer multiple of 2π, dramatically suppresses the correlations in the shot noise.
We examine spin current generated by quantum dots coupled to quantized bosonic field. The dots ar... more We examine spin current generated by quantum dots coupled to quantized bosonic field. The dots are connected to normal leads at zero bias voltage across the dot. We model the dot as a two level spin system with one of the spin states lying below the Fermi level of the leads and the other above. Spin flips followed by subsequent tunnelling out into the leads generate a pure spin current in the absence of any charge current. The dot is coupled to a quantized bosonic field that influences the generation of spin current in one of two possible scenarios. First, we consider spin flips induced via Raman transitions in optical microcavity. Secondly, electron spin resonance via classical magnetic field induces spin flips in the presence of a quantized phonon field that modulates the energy levels of the dot. In the limit of strong Coulomb blockade our model is analogous to the Jaynes-Cummings model in quantum optics. In the case of optical cavity mediated spin flips, we show that the spin current is bistable for a coherently driven cavity and this bistability is clearly visible in the spin current shot noise. A comparison of spin current and shot noise for interactions with different bosonic fields is presented.
In many experiments involving conversion of quantum degenerate atomic gases into molecular dimers... more In many experiments involving conversion of quantum degenerate atomic gases into molecular dimers via a Feshbach resonance, an external magnetic field is linearly swept from above the resonance to below resonance. In the adiabatic limit, the fraction of atoms converted into molecules is independent of the functional form of the sweep and is predicted to be 100%. However, for nonadiabatic sweeps through resonance, Landau-Zener theory predicts that a linear sweep will result in a negligible production of molecules. Here we employ a genetic algorithm to determine the functional time dependence of the magnetic field that produces the maximum number of molecules for sweep times that are comparable to the period of resonant atom-molecule oscillations, 2πΩ −1
We study the photo-association of Bose-Einstein condensed atoms into molecules using a quantized ... more We study the photo-association of Bose-Einstein condensed atoms into molecules using a quantized cavity field. The semiclassical stationary solutions for the three nonlinearly coupled bosonic fields are found and their stability and scaling properties in terms of physical parameters are determined. The full quantum dynamics are simulated using the positive-P distribution and a reduced dynamics in terms of molecule fraction and relative phase between atoms and molecules, which can be mapped onto a Bloch-sphere. Quantum effects at the cross over from stable steady state behavior to large amplitude nonlinear Rabi-oscillations as a function of particle number and inter-particle interaction strengths are investigated.
In many experiments involving conversion of quantum degenerate atomic gases into molecular dimers... more In many experiments involving conversion of quantum degenerate atomic gases into molecular dimers via a Feshbach resonance, an external magnetic field is linearly swept from above the resonance to below resonance. In the adiabatic limit, the fraction of atoms converted into molecules is independent of the functional form of the sweep and is predicted to be 100%. However, for nonadiabatic sweeps through resonance, Landau-Zener theory predicts that a linear sweep will result in a negligible production of molecules. Here we employ a genetic algorithm to determine the functional time dependence of the magnetic field that produces the maximum number of molecules for sweep times that are comparable to the period of resonant atom-molecule oscillations, 2πΩ −1
In many experiments involving conversion of quantum degenerate atomic gases into molecular dimers... more In many experiments involving conversion of quantum degenerate atomic gases into molecular dimers via a Feshbach resonance, an external magnetic field is linearly swept from above the resonance to below resonance. In the adiabatic limit, the fraction of atoms converted into molecules is independent of the functional form of the sweep and is predicted to be 100%. However, for nonadiabatic sweeps through resonance, Landau-Zener theory predicts that a linear sweep will result in a negligible production of molecules. Here we employ a genetic algorithm to determine the functional time dependence of the magnetic field that produces the maximum number of molecules for sweep times that are comparable to the period of resonant atom-molecule oscillations, 2πΩ −1
We examine a ballistic electron Aharonov-Bohm interferometer with a single dot embedded in each o... more We examine a ballistic electron Aharonov-Bohm interferometer with a single dot embedded in each of two arms that are connected in parallel to leads allowing the flow of current by sequential tunneling of electrons through the dots. We focus on the effect that correlations between dots due to the inter-dot spin-spin interactions have on the current-voltage(I-V) and frequency dependent current shot noise. The inter-dot spin-spin interaction is created by embedding the interferometer in an optical microcavity whose modes are far off-resonant with the intra-dot transitions and allows for a cavity mediated exchange of virtual photons between dots. With proper AB phase, inter-dot Coulomb repulsion, and inter-dot cavity mediated coupling, we can control the probability amplitudes for different tunneling paths of the interferometer and the probability of formation of inter-dot entangled spin triplet/singlet states. We analyze the dual effects of inter-dot cavity coupling and two-path interference on the I-V characteristics and shot noise correlations for charge and spin resolved currents in order to determine the conditions for optimal spin triplet/singlet state formation and how they are revealed in the current and noise. We also quantify the level of entanglement between the dots and investigate correlation of shot noise with entanglement measures.
The Sagnac effect is an important phase coherent effect in optical and atom interferometers where... more The Sagnac effect is an important phase coherent effect in optical and atom interferometers where rotations of the interferometer with respect to an inertial reference frame result in a shift in the interference pattern proportional to the rotation rate. Here we analyze for the first time the Sagnac effect in a mesoscopic semiconductor electron interferometer. We include in our analysis Rashba spin-orbit interactions in the ring. Our results indicate that spin-orbit interactions increase the rotation induced phase shift. We discuss the potential experimental observability of the Sagnac phase shift in such mesoscopic systems. PACS numbers: 73.23.-b, 03.75.-b, 72.25.Dc
Here we explore spin dependent quantum transport through a single quantum dot coupled to an optic... more Here we explore spin dependent quantum transport through a single quantum dot coupled to an optical microcavity. The spin current is generated by electron tunneling between a single doped reservoir and the dot combined with intradot spin flip transitions induced by a quantized cavity mode. In the limit of strong Coulomb blockade, this model is analogous to the Jaynes-Cummings model in quantum optics and generates a pure spin current in the absence of any charge current. Earlier research has shown that in the classical limit where a large number of such dots interact with the cavity field, the spin current exhibits bistability as a function of the laser amplitude that drives the cavity. We show that in the limit of a single quantum dot this bistability continues to be present in the intracavity photon statistics. Signatures of the bistable photon statistics manifest themselves in the frequency dependent shot noise of the spin current despite the fact that the quantum mechanical average spin current no longer exhibits bistability. Besides having significance for future quantum dot based optoelectronic devices, our results shed light on the relation between bistability, which is traditionally viewed as a classical effect, and quantum mechanics.
The Sagnac effect is an important phase coherent effect in optical and atom interferometers where... more The Sagnac effect is an important phase coherent effect in optical and atom interferometers where rotations of the interferometer with respect to an inertial reference frame result in a shift in the interference pattern proportional to the rotation rate. Here we analyze for the first time the Sagnac effect in a mesoscopic semiconductor electron interferometer. We include in our analysis Rashba spin-orbit interactions in the ring. Our results indicate that spin-orbit interactions increase the rotation induced phase shift. We discuss the potential experimental observability of the Sagnac phase shift in such mesoscopic systems. PACS numbers: 73.23.-b, 03.75.-b, 72.25.Dc
We examine the spin current and the associated shot noise generated in a quantum dot connected to... more We examine the spin current and the associated shot noise generated in a quantum dot connected to normal leads with zero bias voltage across the dot. The spin current is generated by spin flip transitions induced by a quantized electromagnetic field inside a cavity with one of the Zeeman states lying below the Fermi level of the leads and the other above. In the limit of strong Coulomb blockade, this model is analogous to the Jaynes-Cummings model in quantum optics. We also calculate the photon current and photon current shot noise resulting from photons leaking out of the cavity. We show that the photon current is equal to the spin current and that the spin current can be significantly larger than for the case of a classical driving field as a result of cavity losses. In addition to this, the frequency dependent spin (photon) current shot noise show dips (peaks) that are a result of the discrete nature of photons.
We examine an electron Aharonov-Bohm (AB) interferometer with individual quantum dots connected i... more We examine an electron Aharonov-Bohm (AB) interferometer with individual quantum dots connected in parallel to macroscopic leads. Here, we focus on the effect that both interdot spin-spin exchange interactions and intradot spin flips have on the current- and frequency-dependent current shot noise. By appropriate control of AB magnetic flux, interdot Coulomb repulsion, intradot spin flips, and interdot spin-spin coupling, the probability amplitudes for the different paths of the interferometer can be controlled, leading to broad tunability of both the shape and the contrast of interference fringes in the current. We also show that in the shot noise at finite frequencies corresponding to the spin-spin interaction energies, the noise shows a pronounced super-Poissonian and sub-Poissonian structure. AB flux, which is not an integer multiple of 2π, dramatically suppresses the correlations in the shot noise.
We examine spin current generated by quantum dots coupled to quantized bosonic field. The dots ar... more We examine spin current generated by quantum dots coupled to quantized bosonic field. The dots are connected to normal leads at zero bias voltage across the dot. We model the dot as a two level spin system with one of the spin states lying below the Fermi level of the leads and the other above. Spin flips followed by subsequent tunnelling out into the leads generate a pure spin current in the absence of any charge current. The dot is coupled to a quantized bosonic field that influences the generation of spin current in one of two possible scenarios. First, we consider spin flips induced via Raman transitions in optical microcavity. Secondly, electron spin resonance via classical magnetic field induces spin flips in the presence of a quantized phonon field that modulates the energy levels of the dot. In the limit of strong Coulomb blockade our model is analogous to the Jaynes-Cummings model in quantum optics. In the case of optical cavity mediated spin flips, we show that the spin current is bistable for a coherently driven cavity and this bistability is clearly visible in the spin current shot noise. A comparison of spin current and shot noise for interactions with different bosonic fields is presented.
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