Journal of Physics B: Atomic, Molecular and Optical Physics, 2018
A novel laser cooling mechanism based on many body effects is presented. The method can be applic... more A novel laser cooling mechanism based on many body effects is presented. The method can be applicable for cooling a large class of atoms and molecules in higher density than commonly excepted by existing methods. The cooling mechanism relies on the collective encounters of particle and light. Stochastic events between the particles and photons as well as a collective effect give rise to energy transfer between these media. Such mechanism relies on multiple light-matter encounters, therefore requiring a sufficient particle density, ρ ∼ 10 14 cm −3. This is an advantage for experiments where high phase space density is required. A second tuning laser can be added increasing the applicability to many types of atoms and molecules. This tuning laser changes the inter-particle potential by inducing an AC stark effect. As a result the required trapping density can be reduced down to ρ ∼ 10 6 cm −3. Simulations of phase space distributions were performed comparing different particle densities, trap potentials and light field intensity profiles. The modelling shows efficient cooling rates up to 10 2 K/s for a dense ensemble of 87 Rb atoms, and cooling rates up to 6 • 10 2 K/s when adding an additional tuning source.
A novel laser cooling mechanism based on many body effects is presented. The method can be applic... more A novel laser cooling mechanism based on many body effects is presented. The method can be applicable for cooling a large class of atoms and molecules in higher density than commonly excepted by existing methods. The cooling mechanism relies on the collective encounters of particle and light. Stochastic events between the particles and photons as well as a collective effect give rise to energy transfer between these media. Such mechanism relies on multiple light-matter encounters, therefore requiring a sufficient particle density, ρ ∼ 10 14 cm -3 . This is an advantage for experiments where high phase space density is required. A second tuning laser can be added increasing the applicability to many types of atoms and molecules. This tuning laser changes the inter-particle potential by inducing an AC stark effect. As a result the required trapping density can be reduced down to ρ ∼ 10 6 cm -3 . Simulations of phase space distributions were performed comparing different particle densities, trap potentials and light field intensity profiles. The modelling shows efficient cooling rates up to 10 2 K/s for a dense ensemble of 87 Rb atoms, and cooling rates up to 6 • 10 2 K/s when adding an additional tuning source.
An efficient algorithm to simulate dynamics of open quantum system is presented. The method descr... more An efficient algorithm to simulate dynamics of open quantum system is presented. The method describes the dynamics by unraveling stochastic wave functions converging to a density operator description. The stochastic techniques are based on the quantum collision model. Modeling systems dynamics with wave functions and modeling the interaction with the environment with a collision sequence reduces the scale of the complexity significantly. The algorithm developed can be implemented on quantum computers. We introduce stochastic methods that exploit statistical characteristics of the model such as Markovianity, Brownian motion, and binary distribution. The central limit theorem is employed to study the convergence of distributions of stochastic dynamics of pure quantum states represented by wave vectors. By averaging a sample of functions in the distribution we prove and demonstrate the convergence of the dynamics to the mixed quantum state described by a density operator.
Markovian dynamics of open quantum systems are described by the L-GKS equation, known also as the... more Markovian dynamics of open quantum systems are described by the L-GKS equation, known also as the Lindblad equation. The equation is expressed by means of left and right matrix multiplications. This formulation hampers numerical implementations. Representing the dynamics by a matrix-vector notation overcomes this problem. We review three approaches to obtain such a representation. The methods are demonstrated for a driven two-level system subject to spontaneous emission.
Simulating photo-dissociation processes is a challenging task when the number of states involved ... more Simulating photo-dissociation processes is a challenging task when the number of states involved becomes significantly large. Typically, the computation complexity is reduced by enforcing restrictions that limit the scope of the model. We present an ab-initio quantum model for strong field photo-dissociation processes which incorporates explicitly rotational dynamics. The large computational complexity was reduced by employing the random phase thermal wavefunction method. The simulation outcome are analogous to experimental observables, such as the momentum angular distribution of the photo-fragments. The present work focuses on studying the convergence of such observables at two different field intensities. The simulation method can be applied to wide-ranging time-domain spectroscopy at experimental conditions far beyond the reach of accurate exact numerical methods. In addition to the conventional dependency on the system's size and the number of realizations, the convergence of the method is found to depend on the level of coherence of the simulated observable.
Quantum optimal control, a toolbox for devising and implementing the shapes of external fields th... more Quantum optimal control, a toolbox for devising and implementing the shapes of external fields that accomplish given tasks in the operation of a quantum device in the best way possible, has evolved into one of the cornerstones for enabling quantum technologies. The last few years have seen a rapid evolution and expansion of the field. We review here recent progress in our understanding of the controllability of open quantum systems and in the development and application of quantum control techniques to quantum technologies. We also address key challenges and sketch a roadmap for future developments.
We analyze different decoherence processes in a system coupled to a bath. Apart from the well kno... more We analyze different decoherence processes in a system coupled to a bath. Apart from the well known standard dephasing mechanism which is temperature dependent an alternative mechanism is presented, the spin-swap dephasing which does not need initial bath activation and is temperature independent. We show that for dipolar interaction the separation of time scales between system and bath can not produce pure dephasing, the process being accompained by dissipation. Activated and non activated dephasing processes are demonstrated in a diamond nitrogen-vacancy (NV) center.
Journal of Physics B: Atomic, Molecular and Optical Physics, 2021
Quantum coherent control of ultrafast bond making and the subsequent molecular dynamics is crucia... more Quantum coherent control of ultrafast bond making and the subsequent molecular dynamics is crucial for the realization of a new photochemistry, where a shaped laser field is actively driving the chemical system in a coherent way from the thermal initial state of the reactants to the final state of the desired products. We demonstrate here coherent control over the relative yields of Mg 2 molecules that are generated via photoassociation and subsequently photodriven into different groups of final states. The strong-field process involves non-resonant multiphoton femtosecond photoassociation of a pair of thermally hot magnesium atoms into a bound Mg 2 molecule and subsequent molecular dynamics on electronically excited states. The branching-ratio control is achieved with linearly chirped laser pulses, utilizing the different chirp dependence that various groups of final molecular states display for their post-pulse population. Our study establishes the feasibility of high degree coherent control over quantum molecular dynamics that is initiated by femtosecond photoassociation of thermal atoms.
An experiment based on a trapped Ytterbium ion validates the inertial theorem for the SU (2) alge... more An experiment based on a trapped Ytterbium ion validates the inertial theorem for the SU (2) algebra. The qubit is encoded within the hyperfine states of the atom and controlled by RF fields. The inertial theorem generates an analytical solution for non-adiabatically driven systems that are 'accelerated' slowly, bridging the gap between the sudden and adiabatic limits. These solutions are shown to be stable to small deviations, both experimentally and theoretically. As a result, the inertial solutions pave the way to rapid quantum control of closed, as well as open quantum systems. For large deviations from the inertial condition, the amplitude diverges while the phase remains accurate.
Photoassociation of ultracold atoms with pulsed laser light is shown to lead to alignment of the ... more Photoassociation of ultracold atoms with pulsed laser light is shown to lead to alignment of the product molecules along the excitation laser polarization axis. We theoretically investigate pulsed two-photon photoassociation of 87 Rb atoms into a specific weakly-bound level of the a 3 Σ + u metastable electronic state and find both stationary and time-dependent field-free alignment. Although a transform-limited pulse yields significant alignment, a frequency-chirped pulse dramatically enhances the ultracold molecular formation rate at the cost of a slight decrease in the alignment. Employing multiple pulses synchronized with the vibrational and rotational periods leads to coherent enhancement of both population and alignment of the target state. Inclusion of the rotational degree of freedom in the model gives rise to processes with multiple quantum paths, which lead to quantum effects such as interference and coherence revivals.
Quantum Thermodynamics is a continuous dialogue between two independent theories: Thermodynamics ... more Quantum Thermodynamics is a continuous dialogue between two independent theories: Thermodynamics and Quantum Mechanics. Whenever the two theories have addressed the same phenomena new insight has emerged. We follow the dialogue from equilibrium Quantum Thermodynamics and the notion of entropy and entropy inequalities which are the base of the II-law. Dynamical considerations lead to nonequilibrium thermodynamics of quantum Open Systems. The central part played by completely positive maps is discussed leading to the Gorini-Kossakowski-Lindblad-Sudarshan "GKLS" equation. We address the connection to thermodynamics through the system-bath weak-coupling-limit WCL leading to dynamical versions of the I-law. The dialogue has developed through the analysis of quantum engines and refrigerators. Reciprocating and continuous engines are discussed. The autonomous quantum absorption refrigerator is employed to illustrate the III-law. Finally, we describe some open questions and perspectives.
Dissociation in a strong field: a quantum analysis of the relations between angular momentum and ... more Dissociation in a strong field: a quantum analysis of the relations between angular momentum and angular distribution of fragments.
Quantum Szilard engine constitutes an adequate interplay of thermodynamics, information theory an... more Quantum Szilard engine constitutes an adequate interplay of thermodynamics, information theory and quantum mechanics. Szilard engines are in general operated by a Maxwell’s Demon where Landauer’s principle resolves the apparent paradoxes. Here we propose a Szilard engine setup without featuring an explicit Maxwell’s demon. In a demonless Szilard engine, the acquisition of which-side information is not required, but the erasure and related heat dissipation still take place implicitly. We explore a quantum Szilard engine considering quantum size effects. We see that insertion of the partition does not localize the particle to one side, instead creating a superposition state of the particle being in both sides. To be able to extract work from the system, particle has to be localized at one side. The localization occurs as a result of quantum measurement on the particle, which shows the importance of the measurement process regardless of whether one uses the acquired information or not....
The Carnot cycle combines reversible isothermal and adiabatic strokes to obtain optimal efficienc... more The Carnot cycle combines reversible isothermal and adiabatic strokes to obtain optimal efficiency, at the expense of a vanishing power output. Quantum Carnot-analog cycles are constructed and solved, operating irreversibly with positive power. Swift thermalization is obtained in the isotherms utilizing shortcut to equilibrium protocols and the adiabats employ frictionless unitary shortcuts. The working medium in this study is composed of a particle in a driven harmonic trap. For this system, we solve the dynamics employing a generalized canonical state. Such a description incorporates both changes in energy and coherence. This allows comparing three types of Carnot-analog cycles, Carnot-shortcut, Endo-shortcut and Endo-global. The Carnot-shortcut engine demonstrates the trade-off between power and efficiency. It posses a maximum in power, a minimum cycle-time where it becomes a dissipator and for a diverging cycle-time approaches the ideal Carnot efficiency. The irreversibility of ...
Coherence is associated with transient quantum states; in contrast, equilibrium thermal quantum s... more Coherence is associated with transient quantum states; in contrast, equilibrium thermal quantum systems have no coherence. We investigate the quantum control task of generating maximum coherence from an initial thermal state employing an external field. A completely controllable Hamiltonian is assumed allowing the generation of all possible unitary transformations. Optimizing the unitary control to achieve maximum coherence leads to a micro-canonical energy distribution on the diagonal energy representation. We demonstrate such a control scenario starting from a given Hamiltonian applying an external field, reaching the control target. Such an optimization task is found to be trap-less. By constraining the amount of energy invested by the control, maximum coherence leads to a canonical energy population distribution. When the optimization procedure constrains the final energy too tightly, local suboptimal traps are found. The global optimum is obtained when a small Lagrange multipli...
View the article online for updates and enhancements. Related content Maximizing entanglement in ... more View the article online for updates and enhancements. Related content Maximizing entanglement in bosonic Josephson junctions using shortcuts to adiabaticity and optimal control Dionisis Stefanatos and Emmanuel Paspalakis-Shortcuts to adiabaticity for an ion in a rotating radially-tight trap M Palmero, Shuo Wang, D Guéry-Odelin et al.-Verification of the quantum nonequilibrium work relation in the presence of decoherence Andrew Smith, Yao Lu, Shuoming An et al.
Subrotational cooling of the AlH + ion to the miliKelvin regime, using optimally shaped pulses, i... more Subrotational cooling of the AlH + ion to the miliKelvin regime, using optimally shaped pulses, is computed. The coherent electromagnetic fields induce purity-conserved transformations and do not change the sample temperature. A decrease in a sample temperature, manifested by an increase of purity, is achieved by the complementary uncontrolled spontaneous emission which changes the entropy of the system. We employ optimal control theory to find a pulse that stirs the system into a population configuration that will result in cooling, upon multicycle excitation-emission steps. The obtained optimal transformation was shown capable to cool molecular ions to the subkelvins regime.
We show that the inability of a quantum Otto cycle to reach a limit cycle is connected with the p... more We show that the inability of a quantum Otto cycle to reach a limit cycle is connected with the propagator of the cycle being non-compact. For a working fluid consisting of quantum harmonic oscillators, the transition point in parameter space where this instability occurs is associated with a non-hermitian degeneracy (exceptional point) of the eigenvalues of the propagator. In particular, a third-order exceptional point is observed at the transition from the region where the eigenvalues are complex numbers to the region where all the eigenvalues are real. Within this region we find another exceptional point, this time of second order, at which the trajectory becomes divergent. The onset of the divergent behavior corresponds to the modulus of one of the eigenvalues becoming larger than one. The physical origin of this phenomenon is that the hot and cold heat baths are unable to dissipate the frictional internal heat generated in the adiabatic strokes of the cycle. This behavior is contrasted with that of quantum spins as working fluid which have a compact Hamiltonian and thus no exceptional points. All arguments are rigorously proved in terms of the systems' associated Lie algebras.
Pentaerythritol tetranitrate (PETN) finds many uses in the energetic materials community. Due to ... more Pentaerythritol tetranitrate (PETN) finds many uses in the energetic materials community. Due to the recent availability of erythritol, erythritol tetranitrate (ETN) can now be readily synthesized. Accordingly, its complete characterization, especially its stability, is of great interest. This work examines the thermal decomposition of ETN, both through experimental and computational methods. In addition to kinetic parameters, decomposition products were examined to elucidate its decomposition pathway. It is found that ETN begins its decomposition sequence by a unimolecular homolytic cleavage of the internal and external O−NO 2 bonds, while the competing HONO elimination reaction is largely suppressed. The global activation energy for decomposition is found to be 104.3 kJ/mol with a pre-exponential factor of 3.72 × 10 9 s −1. Despite the ability to exist in a molten state, ETN has a lower thermal stability than its counterpart PETN.
We describe experiments and associated quantum simulations involving the production of ultracold ... more We describe experiments and associated quantum simulations involving the production of ultracold 87 Rb 2 molecules with nanosecond pulses of frequency-chirped light. With appropriate chirp parameters, the formation is dominated by coherent processes. For a positive chirp, excited molecules are produced by photoassociation early in the chirp, then transferred into high vibrational levels of the lowest triplet state by stimulated emission later in the chirp. Generally good agreement is seen between the data and the simulations. Shaping of the chirp can lead to a significant enhancement of the formation rate. Further improvements using higher intensities and different intermediate states are predicted.
Journal of Physics B: Atomic, Molecular and Optical Physics, 2018
A novel laser cooling mechanism based on many body effects is presented. The method can be applic... more A novel laser cooling mechanism based on many body effects is presented. The method can be applicable for cooling a large class of atoms and molecules in higher density than commonly excepted by existing methods. The cooling mechanism relies on the collective encounters of particle and light. Stochastic events between the particles and photons as well as a collective effect give rise to energy transfer between these media. Such mechanism relies on multiple light-matter encounters, therefore requiring a sufficient particle density, ρ ∼ 10 14 cm −3. This is an advantage for experiments where high phase space density is required. A second tuning laser can be added increasing the applicability to many types of atoms and molecules. This tuning laser changes the inter-particle potential by inducing an AC stark effect. As a result the required trapping density can be reduced down to ρ ∼ 10 6 cm −3. Simulations of phase space distributions were performed comparing different particle densities, trap potentials and light field intensity profiles. The modelling shows efficient cooling rates up to 10 2 K/s for a dense ensemble of 87 Rb atoms, and cooling rates up to 6 • 10 2 K/s when adding an additional tuning source.
A novel laser cooling mechanism based on many body effects is presented. The method can be applic... more A novel laser cooling mechanism based on many body effects is presented. The method can be applicable for cooling a large class of atoms and molecules in higher density than commonly excepted by existing methods. The cooling mechanism relies on the collective encounters of particle and light. Stochastic events between the particles and photons as well as a collective effect give rise to energy transfer between these media. Such mechanism relies on multiple light-matter encounters, therefore requiring a sufficient particle density, ρ ∼ 10 14 cm -3 . This is an advantage for experiments where high phase space density is required. A second tuning laser can be added increasing the applicability to many types of atoms and molecules. This tuning laser changes the inter-particle potential by inducing an AC stark effect. As a result the required trapping density can be reduced down to ρ ∼ 10 6 cm -3 . Simulations of phase space distributions were performed comparing different particle densities, trap potentials and light field intensity profiles. The modelling shows efficient cooling rates up to 10 2 K/s for a dense ensemble of 87 Rb atoms, and cooling rates up to 6 • 10 2 K/s when adding an additional tuning source.
An efficient algorithm to simulate dynamics of open quantum system is presented. The method descr... more An efficient algorithm to simulate dynamics of open quantum system is presented. The method describes the dynamics by unraveling stochastic wave functions converging to a density operator description. The stochastic techniques are based on the quantum collision model. Modeling systems dynamics with wave functions and modeling the interaction with the environment with a collision sequence reduces the scale of the complexity significantly. The algorithm developed can be implemented on quantum computers. We introduce stochastic methods that exploit statistical characteristics of the model such as Markovianity, Brownian motion, and binary distribution. The central limit theorem is employed to study the convergence of distributions of stochastic dynamics of pure quantum states represented by wave vectors. By averaging a sample of functions in the distribution we prove and demonstrate the convergence of the dynamics to the mixed quantum state described by a density operator.
Markovian dynamics of open quantum systems are described by the L-GKS equation, known also as the... more Markovian dynamics of open quantum systems are described by the L-GKS equation, known also as the Lindblad equation. The equation is expressed by means of left and right matrix multiplications. This formulation hampers numerical implementations. Representing the dynamics by a matrix-vector notation overcomes this problem. We review three approaches to obtain such a representation. The methods are demonstrated for a driven two-level system subject to spontaneous emission.
Simulating photo-dissociation processes is a challenging task when the number of states involved ... more Simulating photo-dissociation processes is a challenging task when the number of states involved becomes significantly large. Typically, the computation complexity is reduced by enforcing restrictions that limit the scope of the model. We present an ab-initio quantum model for strong field photo-dissociation processes which incorporates explicitly rotational dynamics. The large computational complexity was reduced by employing the random phase thermal wavefunction method. The simulation outcome are analogous to experimental observables, such as the momentum angular distribution of the photo-fragments. The present work focuses on studying the convergence of such observables at two different field intensities. The simulation method can be applied to wide-ranging time-domain spectroscopy at experimental conditions far beyond the reach of accurate exact numerical methods. In addition to the conventional dependency on the system's size and the number of realizations, the convergence of the method is found to depend on the level of coherence of the simulated observable.
Quantum optimal control, a toolbox for devising and implementing the shapes of external fields th... more Quantum optimal control, a toolbox for devising and implementing the shapes of external fields that accomplish given tasks in the operation of a quantum device in the best way possible, has evolved into one of the cornerstones for enabling quantum technologies. The last few years have seen a rapid evolution and expansion of the field. We review here recent progress in our understanding of the controllability of open quantum systems and in the development and application of quantum control techniques to quantum technologies. We also address key challenges and sketch a roadmap for future developments.
We analyze different decoherence processes in a system coupled to a bath. Apart from the well kno... more We analyze different decoherence processes in a system coupled to a bath. Apart from the well known standard dephasing mechanism which is temperature dependent an alternative mechanism is presented, the spin-swap dephasing which does not need initial bath activation and is temperature independent. We show that for dipolar interaction the separation of time scales between system and bath can not produce pure dephasing, the process being accompained by dissipation. Activated and non activated dephasing processes are demonstrated in a diamond nitrogen-vacancy (NV) center.
Journal of Physics B: Atomic, Molecular and Optical Physics, 2021
Quantum coherent control of ultrafast bond making and the subsequent molecular dynamics is crucia... more Quantum coherent control of ultrafast bond making and the subsequent molecular dynamics is crucial for the realization of a new photochemistry, where a shaped laser field is actively driving the chemical system in a coherent way from the thermal initial state of the reactants to the final state of the desired products. We demonstrate here coherent control over the relative yields of Mg 2 molecules that are generated via photoassociation and subsequently photodriven into different groups of final states. The strong-field process involves non-resonant multiphoton femtosecond photoassociation of a pair of thermally hot magnesium atoms into a bound Mg 2 molecule and subsequent molecular dynamics on electronically excited states. The branching-ratio control is achieved with linearly chirped laser pulses, utilizing the different chirp dependence that various groups of final molecular states display for their post-pulse population. Our study establishes the feasibility of high degree coherent control over quantum molecular dynamics that is initiated by femtosecond photoassociation of thermal atoms.
An experiment based on a trapped Ytterbium ion validates the inertial theorem for the SU (2) alge... more An experiment based on a trapped Ytterbium ion validates the inertial theorem for the SU (2) algebra. The qubit is encoded within the hyperfine states of the atom and controlled by RF fields. The inertial theorem generates an analytical solution for non-adiabatically driven systems that are 'accelerated' slowly, bridging the gap between the sudden and adiabatic limits. These solutions are shown to be stable to small deviations, both experimentally and theoretically. As a result, the inertial solutions pave the way to rapid quantum control of closed, as well as open quantum systems. For large deviations from the inertial condition, the amplitude diverges while the phase remains accurate.
Photoassociation of ultracold atoms with pulsed laser light is shown to lead to alignment of the ... more Photoassociation of ultracold atoms with pulsed laser light is shown to lead to alignment of the product molecules along the excitation laser polarization axis. We theoretically investigate pulsed two-photon photoassociation of 87 Rb atoms into a specific weakly-bound level of the a 3 Σ + u metastable electronic state and find both stationary and time-dependent field-free alignment. Although a transform-limited pulse yields significant alignment, a frequency-chirped pulse dramatically enhances the ultracold molecular formation rate at the cost of a slight decrease in the alignment. Employing multiple pulses synchronized with the vibrational and rotational periods leads to coherent enhancement of both population and alignment of the target state. Inclusion of the rotational degree of freedom in the model gives rise to processes with multiple quantum paths, which lead to quantum effects such as interference and coherence revivals.
Quantum Thermodynamics is a continuous dialogue between two independent theories: Thermodynamics ... more Quantum Thermodynamics is a continuous dialogue between two independent theories: Thermodynamics and Quantum Mechanics. Whenever the two theories have addressed the same phenomena new insight has emerged. We follow the dialogue from equilibrium Quantum Thermodynamics and the notion of entropy and entropy inequalities which are the base of the II-law. Dynamical considerations lead to nonequilibrium thermodynamics of quantum Open Systems. The central part played by completely positive maps is discussed leading to the Gorini-Kossakowski-Lindblad-Sudarshan "GKLS" equation. We address the connection to thermodynamics through the system-bath weak-coupling-limit WCL leading to dynamical versions of the I-law. The dialogue has developed through the analysis of quantum engines and refrigerators. Reciprocating and continuous engines are discussed. The autonomous quantum absorption refrigerator is employed to illustrate the III-law. Finally, we describe some open questions and perspectives.
Dissociation in a strong field: a quantum analysis of the relations between angular momentum and ... more Dissociation in a strong field: a quantum analysis of the relations between angular momentum and angular distribution of fragments.
Quantum Szilard engine constitutes an adequate interplay of thermodynamics, information theory an... more Quantum Szilard engine constitutes an adequate interplay of thermodynamics, information theory and quantum mechanics. Szilard engines are in general operated by a Maxwell’s Demon where Landauer’s principle resolves the apparent paradoxes. Here we propose a Szilard engine setup without featuring an explicit Maxwell’s demon. In a demonless Szilard engine, the acquisition of which-side information is not required, but the erasure and related heat dissipation still take place implicitly. We explore a quantum Szilard engine considering quantum size effects. We see that insertion of the partition does not localize the particle to one side, instead creating a superposition state of the particle being in both sides. To be able to extract work from the system, particle has to be localized at one side. The localization occurs as a result of quantum measurement on the particle, which shows the importance of the measurement process regardless of whether one uses the acquired information or not....
The Carnot cycle combines reversible isothermal and adiabatic strokes to obtain optimal efficienc... more The Carnot cycle combines reversible isothermal and adiabatic strokes to obtain optimal efficiency, at the expense of a vanishing power output. Quantum Carnot-analog cycles are constructed and solved, operating irreversibly with positive power. Swift thermalization is obtained in the isotherms utilizing shortcut to equilibrium protocols and the adiabats employ frictionless unitary shortcuts. The working medium in this study is composed of a particle in a driven harmonic trap. For this system, we solve the dynamics employing a generalized canonical state. Such a description incorporates both changes in energy and coherence. This allows comparing three types of Carnot-analog cycles, Carnot-shortcut, Endo-shortcut and Endo-global. The Carnot-shortcut engine demonstrates the trade-off between power and efficiency. It posses a maximum in power, a minimum cycle-time where it becomes a dissipator and for a diverging cycle-time approaches the ideal Carnot efficiency. The irreversibility of ...
Coherence is associated with transient quantum states; in contrast, equilibrium thermal quantum s... more Coherence is associated with transient quantum states; in contrast, equilibrium thermal quantum systems have no coherence. We investigate the quantum control task of generating maximum coherence from an initial thermal state employing an external field. A completely controllable Hamiltonian is assumed allowing the generation of all possible unitary transformations. Optimizing the unitary control to achieve maximum coherence leads to a micro-canonical energy distribution on the diagonal energy representation. We demonstrate such a control scenario starting from a given Hamiltonian applying an external field, reaching the control target. Such an optimization task is found to be trap-less. By constraining the amount of energy invested by the control, maximum coherence leads to a canonical energy population distribution. When the optimization procedure constrains the final energy too tightly, local suboptimal traps are found. The global optimum is obtained when a small Lagrange multipli...
View the article online for updates and enhancements. Related content Maximizing entanglement in ... more View the article online for updates and enhancements. Related content Maximizing entanglement in bosonic Josephson junctions using shortcuts to adiabaticity and optimal control Dionisis Stefanatos and Emmanuel Paspalakis-Shortcuts to adiabaticity for an ion in a rotating radially-tight trap M Palmero, Shuo Wang, D Guéry-Odelin et al.-Verification of the quantum nonequilibrium work relation in the presence of decoherence Andrew Smith, Yao Lu, Shuoming An et al.
Subrotational cooling of the AlH + ion to the miliKelvin regime, using optimally shaped pulses, i... more Subrotational cooling of the AlH + ion to the miliKelvin regime, using optimally shaped pulses, is computed. The coherent electromagnetic fields induce purity-conserved transformations and do not change the sample temperature. A decrease in a sample temperature, manifested by an increase of purity, is achieved by the complementary uncontrolled spontaneous emission which changes the entropy of the system. We employ optimal control theory to find a pulse that stirs the system into a population configuration that will result in cooling, upon multicycle excitation-emission steps. The obtained optimal transformation was shown capable to cool molecular ions to the subkelvins regime.
We show that the inability of a quantum Otto cycle to reach a limit cycle is connected with the p... more We show that the inability of a quantum Otto cycle to reach a limit cycle is connected with the propagator of the cycle being non-compact. For a working fluid consisting of quantum harmonic oscillators, the transition point in parameter space where this instability occurs is associated with a non-hermitian degeneracy (exceptional point) of the eigenvalues of the propagator. In particular, a third-order exceptional point is observed at the transition from the region where the eigenvalues are complex numbers to the region where all the eigenvalues are real. Within this region we find another exceptional point, this time of second order, at which the trajectory becomes divergent. The onset of the divergent behavior corresponds to the modulus of one of the eigenvalues becoming larger than one. The physical origin of this phenomenon is that the hot and cold heat baths are unable to dissipate the frictional internal heat generated in the adiabatic strokes of the cycle. This behavior is contrasted with that of quantum spins as working fluid which have a compact Hamiltonian and thus no exceptional points. All arguments are rigorously proved in terms of the systems' associated Lie algebras.
Pentaerythritol tetranitrate (PETN) finds many uses in the energetic materials community. Due to ... more Pentaerythritol tetranitrate (PETN) finds many uses in the energetic materials community. Due to the recent availability of erythritol, erythritol tetranitrate (ETN) can now be readily synthesized. Accordingly, its complete characterization, especially its stability, is of great interest. This work examines the thermal decomposition of ETN, both through experimental and computational methods. In addition to kinetic parameters, decomposition products were examined to elucidate its decomposition pathway. It is found that ETN begins its decomposition sequence by a unimolecular homolytic cleavage of the internal and external O−NO 2 bonds, while the competing HONO elimination reaction is largely suppressed. The global activation energy for decomposition is found to be 104.3 kJ/mol with a pre-exponential factor of 3.72 × 10 9 s −1. Despite the ability to exist in a molten state, ETN has a lower thermal stability than its counterpart PETN.
We describe experiments and associated quantum simulations involving the production of ultracold ... more We describe experiments and associated quantum simulations involving the production of ultracold 87 Rb 2 molecules with nanosecond pulses of frequency-chirped light. With appropriate chirp parameters, the formation is dominated by coherent processes. For a positive chirp, excited molecules are produced by photoassociation early in the chirp, then transferred into high vibrational levels of the lowest triplet state by stimulated emission later in the chirp. Generally good agreement is seen between the data and the simulations. Shaping of the chirp can lead to a significant enhancement of the formation rate. Further improvements using higher intensities and different intermediate states are predicted.
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