In order to describe the velocity of two bodies after they collide, Newton developed a phenomenol... more In order to describe the velocity of two bodies after they collide, Newton developed a phenomenological equation known as ‘Newton’s experimental law’ (NEL). In this way, he was able to practically bypass the complication involving the details of the force that occurs during the collision of the two bodies. Today, we use NEL together with momentum conservation to predict each body’s velocity after collision. This, indeed, avoids the complication of knowing the forces involved in the collision, making NEL very useful. Whereas in Newton’s days the quantity of kinetic energy was not known, today it is a basic quantity that is in use. In this paper we will use the loss (or gain) of kinetic energy in a collision to show how NEL can be derived.
We derive rigorously the short-time escape probability of a quantum particle from its compactly s... more We derive rigorously the short-time escape probability of a quantum particle from its compactly supported initial state, which has a discontinuous derivative at the boundary of the support. We show that this probability is linear in time, which seems to be a new result. The novelty of our calculation is the inclusion of the boundary layer of the propagated wave function formed outside the initial support. This result has applications to the decay law of the particle, to the Zeno behaviour, quantum absorption, time of arrival, quantum measurements, and more.
The ability to control and hence to realize a given number of photons is of major interest from a... more The ability to control and hence to realize a given number of photons is of major interest from a fundamental point of view. e.g. Bell inequalities, photons bunching. In recent years this interest has grown by the so called the “Second Quantum Revolution” where such an ability is needed for quantum computers, etc. In this paper we show that such a realization can’t be done by a unitary process. Therefore, a non-unitary interferometer is given to build a full realization of the tensor product space for two photons at two states. Finally, by modifying the previous interferometer, the full tonsorial product space of N photons in two states is shown.
R d −D. The continuous collapse axiom (CCA) defines the post-measurement wave function (PMWF)in D... more R d −D. The continuous collapse axiom (CCA) defines the post-measurement wave function (PMWF)in D after a negative measurement as the solution of Schrödinger’s equation at time τ with instantaneously collapsed initial condition and homogeneous Dirichlet condition on the boundary of D. The CCA applies to all cases that exhibit the Zeno effect. It rids quantum mechanics of the unphysical artifacts caused by instantaneous collapse and introduces no new artifacts.
We investigate the dynamics of pairs of Fermions and Bosons released from a box and find that the... more We investigate the dynamics of pairs of Fermions and Bosons released from a box and find that their populations have unique generic properties ensuing from the axioms of quantum statistics and symmetries. These depend neither on the specific equations of wave function propagation, such as Schr\"odinger, Klein-Gordon, Dirac, nor on the specific potential involved. One surprising finding is that after releasing the pairs, there are always more Boson than Fermion pairs outside the box. Moreover, if the initial wave functions have the same symmetry (odd or even), then there is a higher chance for a Boson than a Fermion pair to escape from the trap in opposite directions, as if they repel each other. We calculate the wave functions exactly, numerically, and asymptotically for short time and demonstrate these generic results in the specific case of particles released from an infinite well.
The effect of boson bunching is frequently mentioned and discussed in the literature. This effect... more The effect of boson bunching is frequently mentioned and discussed in the literature. This effect is the manifestation of bosons tendency to "travel" in clusters. One of the core arguments for boson bunching was formulated by Feynman in his well-known lecture series and has been frequently used ever since. By comparing the scattering probabilities of two bosons and of two non-identical particles, Feynman concluded: "We have the result that it is twice as likely to find two identical Bose particles scattered into the same state as you would calculate assuming the particles were different." [1]. Indeed, in most scenarios, this reasoning is valid, however, as it is shown in this paper, there are cases, even in the most ordinary scattering scenarios, where this reasoning is invalid, and in fact the opposite occurs: boson anti-bunching appears. Similarly, it is shown that at exactly the same scenarios, fermions bunch together.
It is shown that when the initial particles probability density is discontinuous the emerging cur... more It is shown that when the initial particles probability density is discontinuous the emerging currents appear instantaneously, and although the density beyond the discontinuity is initially negligible the currents there have a finite value. It is shown that this non-equilibrium effect can be measured in real experiments (such as cooled Rubidium atoms), where the discontinuity is replaced with finite width
ABSTRACT The Schrödinger evolution of an initially singular wave function was investigated. First... more ABSTRACT The Schrödinger evolution of an initially singular wave function was investigated. First it was shown that a wide range of physical problems can be described by initially singular wave function. Then it was demonstrated that outside the support of the initial wave function the time evolution is governed to leading order by the values of the wave function and its derivatives at the singular points. Short-time universality appears where it depends only on a single parameter—the value at the singular point (not even on its derivatives). It was also demonstrated that the short-time evolution in the presence of an absorptive potential is different than in the presence of a nonabsorptive one. Therefore, this dynamics can be harnessed to the determination whether a potential is absorptive or not simply by measuring only the transmitted particles density.
A general solution to the "shutter" problem is presented. The propagation of an arbitrary initial... more A general solution to the "shutter" problem is presented. The propagation of an arbitrary initially bounded wavefunction is investigated, and the general solution for any such function is formulated. It is shown that the exact solution can be written as an expression that depends only on the values of the function (and its derivatives) at the boundaries. In particular, it is shown that at short times ( h / 2 2 mx t <<
We describe the dynamics of a bound state of an attractive δ-well under displacement of the poten... more We describe the dynamics of a bound state of an attractive δ-well under displacement of the potential. Exact analytical results are presented for the suddenly moved potential. Since this is a quantum system, only a fraction of the initially confined wavefunction remains confined to the moving potential. However, it is shown that besides the probability to remain confined to the moving barrier and the probability to remain in the initial position, there is also a certain probability for the particle to move at double speed. A quasi-classical interpretation for this effect is suggested. The temporal and spectral dynamics of each one of the scenarios is investigated.
We present a general framework to study the effect of killing sources on moving particles, traffi... more We present a general framework to study the effect of killing sources on moving particles, trafficking inside biological cells. We are merely concerned with the case of spine-dendrite communication, where the number of calcium ions, modeled as random particles is regulated across the spine microstructure by pumps, which play the killing role. In particular, we study here the survival probability of ions in such environment and we present a general theory to compute the ratio of the number of absorbed particles at specific location to the number of killed particles during their sojourn inside a domain. In the case of a dendritic spine, the ratio is computed in terms of the survival probability of a stochastic trajectory in a one dimensional approximation. We show that the ratio depends on the distribution of killing sources. The biological conclusion follows: changing the position of the pumps is enough to regulate the calcium ions and thus the spine-dendrite communication.
We show that propagating a truncated discontinuous wave function by Schr\"odinger's equation, as ... more We show that propagating a truncated discontinuous wave function by Schr\"odinger's equation, as asserted by the collapse axiom, gives rise to non-existence of the average displacement of the particle on the line. It also implies that there is no Zeno effect. On the other hand, if the truncation is done so that the reduced wave function is continuous, the average coordinate is finite and there is a Zeno effect. Therefore the collapse axiom of measurement needs to be revised.
ABSTRACT The SCALE-UP program is about devising a new environment for teaching physics. The SCALE... more ABSTRACT The SCALE-UP program is about devising a new environment for teaching physics. The SCALE-UP class consists of 99 students organized into nine groups. Each group sits around a round table where every two or three students share a computer. The class commences with a ten-minute introductory presentation by the instructor, followed by the students&#39; independent work on computer assignments related to the topic. In this talk we will explain the motivation for the SCALE-UP program and its advantages. We will also present a variety of results from research already performed on the SCALE-UP program.
Discontinuous initial wave functions or wave functions with discontintuous derivative and with bo... more Discontinuous initial wave functions or wave functions with discontintuous derivative and with bounded support arise in a natural way in various situations in physics, in particular in measurement theory. The propagation of such initial wave functions is not well described by the Schr\"odinger current which vanishes on the boundary of the support of the wave function. This propagation gives rise to a uni-directional current at the boundary of the support. We use path integrals to define current and uni-directional current and give a direct derivation of the expression for current from the path integral formulation for both diffusion and quantum mechanics. Furthermore, we give an explicit asymptotic expression for the short time propagation of initial wave function with compact support for both the cases of discontinuous derivative and discontinuous wave function. We show that in the former case the probability propagated across the boundary of the support in time $\Delta t$ is $O(\Delta t^{3/2})$ and the initial uni-directional current is $O(\Delta t^{1/2})$. This recovers the Zeno effect for continuous detection of a particle in a given domain. For the latter case the probability propagated across the boundary of the support in time $\Delta t$ is $O(\Delta t^{1/2})$ and the initial uni-directional current is $O(\Delta t^{-1/2})$. This is an anti-Zeno effect. However, the probability propagated across a point located at a finite distance from the boundary of the support is $O(\Delta t)$. This gives a decay law.
Discontinuous initial wave functions, or wave functions with a discontinuous derivative and a bou... more Discontinuous initial wave functions, or wave functions with a discontinuous derivative and a bounded support, arise in a natural way in various situations in physics, in particular in measurement theory. The propagation of such initial wave functions is not well described by the Schrödinger current which vanishes on the boundary of the support of the wave function. This propagation gives rise to a unidirectional current at the boundary of the support. We use path integrals to define current and unidirectional current, and to provide a direct derivation of the expression for current from the path-integral formulation for both diffusion and quantum mechanics. Furthermore, we give an explicit asymptotic expression for the short-time propagation of an initial wave function with compact support for cases of both a discontinuous derivative and a discontinuous wave function. We show that in the former case the probability propagated across the boundary of the support in time Δt is O(Δt3/2), and the initial unidirectional current is O(Δt1/2). This recovers the Zeno effect for continuous detection of a particle in a given domain. For the latter case the probability propagated across the boundary of the support in time Δt is O(Δt1/2), and the initial unidirectional current is O(Δt-1/2). This is an anti-Zeno effect. However, the probability propagated across a point located at a finite distance from the boundary of the support is O(Δt). This gives a decay law.
We propose a formulation of an absorbing boundary for a quantum particle. The formulation is base... more We propose a formulation of an absorbing boundary for a quantum particle. The formulation is based on a Feynman-type integral over trajectories that are confined by the absorbing boundary. Trajectories that reach the absorbing wall are instantaneously terminated and their probability is discounted from the population of the surviving trajectories. This gives rise to a unidirectional absorption current at the boundary. We calculate the survival probability as a function of time. Several modes of absorption are derived from our formalism: total absorption, absorption that depends on energy levels, and absorption of non-interacting particles. Several applications are given: the slit experiment with an absorbing screen and with absorbing lateral walls, and one dimensional particle between two absorbing walls. The survival probability of a particle between absorbing walls exhibits decay with beats.
We consider the evolution of Green's function of the one-dimensional Schr\"odinger equation in th... more We consider the evolution of Green's function of the one-dimensional Schr\"odinger equation in the presence of the complex potential $-ik\delta(x)$. Our result is the construction of an explicit time-dependent solution which we use to calculate the time-dependent survival probability of a quantum particle. The survival probability decays to zero in finite time, which means that the complex delta potential well is a total absorber for quantum particles. This potential can be interpreted as a killing measure with infinite killing rate concentrated at the origin.
In order to describe the velocity of two bodies after they collide, Newton developed a phenomenol... more In order to describe the velocity of two bodies after they collide, Newton developed a phenomenological equation known as ‘Newton’s experimental law’ (NEL). In this way, he was able to practically bypass the complication involving the details of the force that occurs during the collision of the two bodies. Today, we use NEL together with momentum conservation to predict each body’s velocity after collision. This, indeed, avoids the complication of knowing the forces involved in the collision, making NEL very useful. Whereas in Newton’s days the quantity of kinetic energy was not known, today it is a basic quantity that is in use. In this paper we will use the loss (or gain) of kinetic energy in a collision to show how NEL can be derived.
We derive rigorously the short-time escape probability of a quantum particle from its compactly s... more We derive rigorously the short-time escape probability of a quantum particle from its compactly supported initial state, which has a discontinuous derivative at the boundary of the support. We show that this probability is linear in time, which seems to be a new result. The novelty of our calculation is the inclusion of the boundary layer of the propagated wave function formed outside the initial support. This result has applications to the decay law of the particle, to the Zeno behaviour, quantum absorption, time of arrival, quantum measurements, and more.
The ability to control and hence to realize a given number of photons is of major interest from a... more The ability to control and hence to realize a given number of photons is of major interest from a fundamental point of view. e.g. Bell inequalities, photons bunching. In recent years this interest has grown by the so called the “Second Quantum Revolution” where such an ability is needed for quantum computers, etc. In this paper we show that such a realization can’t be done by a unitary process. Therefore, a non-unitary interferometer is given to build a full realization of the tensor product space for two photons at two states. Finally, by modifying the previous interferometer, the full tonsorial product space of N photons in two states is shown.
R d −D. The continuous collapse axiom (CCA) defines the post-measurement wave function (PMWF)in D... more R d −D. The continuous collapse axiom (CCA) defines the post-measurement wave function (PMWF)in D after a negative measurement as the solution of Schrödinger’s equation at time τ with instantaneously collapsed initial condition and homogeneous Dirichlet condition on the boundary of D. The CCA applies to all cases that exhibit the Zeno effect. It rids quantum mechanics of the unphysical artifacts caused by instantaneous collapse and introduces no new artifacts.
We investigate the dynamics of pairs of Fermions and Bosons released from a box and find that the... more We investigate the dynamics of pairs of Fermions and Bosons released from a box and find that their populations have unique generic properties ensuing from the axioms of quantum statistics and symmetries. These depend neither on the specific equations of wave function propagation, such as Schr\"odinger, Klein-Gordon, Dirac, nor on the specific potential involved. One surprising finding is that after releasing the pairs, there are always more Boson than Fermion pairs outside the box. Moreover, if the initial wave functions have the same symmetry (odd or even), then there is a higher chance for a Boson than a Fermion pair to escape from the trap in opposite directions, as if they repel each other. We calculate the wave functions exactly, numerically, and asymptotically for short time and demonstrate these generic results in the specific case of particles released from an infinite well.
The effect of boson bunching is frequently mentioned and discussed in the literature. This effect... more The effect of boson bunching is frequently mentioned and discussed in the literature. This effect is the manifestation of bosons tendency to "travel" in clusters. One of the core arguments for boson bunching was formulated by Feynman in his well-known lecture series and has been frequently used ever since. By comparing the scattering probabilities of two bosons and of two non-identical particles, Feynman concluded: "We have the result that it is twice as likely to find two identical Bose particles scattered into the same state as you would calculate assuming the particles were different." [1]. Indeed, in most scenarios, this reasoning is valid, however, as it is shown in this paper, there are cases, even in the most ordinary scattering scenarios, where this reasoning is invalid, and in fact the opposite occurs: boson anti-bunching appears. Similarly, it is shown that at exactly the same scenarios, fermions bunch together.
It is shown that when the initial particles probability density is discontinuous the emerging cur... more It is shown that when the initial particles probability density is discontinuous the emerging currents appear instantaneously, and although the density beyond the discontinuity is initially negligible the currents there have a finite value. It is shown that this non-equilibrium effect can be measured in real experiments (such as cooled Rubidium atoms), where the discontinuity is replaced with finite width
ABSTRACT The Schrödinger evolution of an initially singular wave function was investigated. First... more ABSTRACT The Schrödinger evolution of an initially singular wave function was investigated. First it was shown that a wide range of physical problems can be described by initially singular wave function. Then it was demonstrated that outside the support of the initial wave function the time evolution is governed to leading order by the values of the wave function and its derivatives at the singular points. Short-time universality appears where it depends only on a single parameter—the value at the singular point (not even on its derivatives). It was also demonstrated that the short-time evolution in the presence of an absorptive potential is different than in the presence of a nonabsorptive one. Therefore, this dynamics can be harnessed to the determination whether a potential is absorptive or not simply by measuring only the transmitted particles density.
A general solution to the "shutter" problem is presented. The propagation of an arbitrary initial... more A general solution to the "shutter" problem is presented. The propagation of an arbitrary initially bounded wavefunction is investigated, and the general solution for any such function is formulated. It is shown that the exact solution can be written as an expression that depends only on the values of the function (and its derivatives) at the boundaries. In particular, it is shown that at short times ( h / 2 2 mx t <<
We describe the dynamics of a bound state of an attractive δ-well under displacement of the poten... more We describe the dynamics of a bound state of an attractive δ-well under displacement of the potential. Exact analytical results are presented for the suddenly moved potential. Since this is a quantum system, only a fraction of the initially confined wavefunction remains confined to the moving potential. However, it is shown that besides the probability to remain confined to the moving barrier and the probability to remain in the initial position, there is also a certain probability for the particle to move at double speed. A quasi-classical interpretation for this effect is suggested. The temporal and spectral dynamics of each one of the scenarios is investigated.
We present a general framework to study the effect of killing sources on moving particles, traffi... more We present a general framework to study the effect of killing sources on moving particles, trafficking inside biological cells. We are merely concerned with the case of spine-dendrite communication, where the number of calcium ions, modeled as random particles is regulated across the spine microstructure by pumps, which play the killing role. In particular, we study here the survival probability of ions in such environment and we present a general theory to compute the ratio of the number of absorbed particles at specific location to the number of killed particles during their sojourn inside a domain. In the case of a dendritic spine, the ratio is computed in terms of the survival probability of a stochastic trajectory in a one dimensional approximation. We show that the ratio depends on the distribution of killing sources. The biological conclusion follows: changing the position of the pumps is enough to regulate the calcium ions and thus the spine-dendrite communication.
We show that propagating a truncated discontinuous wave function by Schr\"odinger's equation, as ... more We show that propagating a truncated discontinuous wave function by Schr\"odinger's equation, as asserted by the collapse axiom, gives rise to non-existence of the average displacement of the particle on the line. It also implies that there is no Zeno effect. On the other hand, if the truncation is done so that the reduced wave function is continuous, the average coordinate is finite and there is a Zeno effect. Therefore the collapse axiom of measurement needs to be revised.
ABSTRACT The SCALE-UP program is about devising a new environment for teaching physics. The SCALE... more ABSTRACT The SCALE-UP program is about devising a new environment for teaching physics. The SCALE-UP class consists of 99 students organized into nine groups. Each group sits around a round table where every two or three students share a computer. The class commences with a ten-minute introductory presentation by the instructor, followed by the students&#39; independent work on computer assignments related to the topic. In this talk we will explain the motivation for the SCALE-UP program and its advantages. We will also present a variety of results from research already performed on the SCALE-UP program.
Discontinuous initial wave functions or wave functions with discontintuous derivative and with bo... more Discontinuous initial wave functions or wave functions with discontintuous derivative and with bounded support arise in a natural way in various situations in physics, in particular in measurement theory. The propagation of such initial wave functions is not well described by the Schr\"odinger current which vanishes on the boundary of the support of the wave function. This propagation gives rise to a uni-directional current at the boundary of the support. We use path integrals to define current and uni-directional current and give a direct derivation of the expression for current from the path integral formulation for both diffusion and quantum mechanics. Furthermore, we give an explicit asymptotic expression for the short time propagation of initial wave function with compact support for both the cases of discontinuous derivative and discontinuous wave function. We show that in the former case the probability propagated across the boundary of the support in time $\Delta t$ is $O(\Delta t^{3/2})$ and the initial uni-directional current is $O(\Delta t^{1/2})$. This recovers the Zeno effect for continuous detection of a particle in a given domain. For the latter case the probability propagated across the boundary of the support in time $\Delta t$ is $O(\Delta t^{1/2})$ and the initial uni-directional current is $O(\Delta t^{-1/2})$. This is an anti-Zeno effect. However, the probability propagated across a point located at a finite distance from the boundary of the support is $O(\Delta t)$. This gives a decay law.
Discontinuous initial wave functions, or wave functions with a discontinuous derivative and a bou... more Discontinuous initial wave functions, or wave functions with a discontinuous derivative and a bounded support, arise in a natural way in various situations in physics, in particular in measurement theory. The propagation of such initial wave functions is not well described by the Schrödinger current which vanishes on the boundary of the support of the wave function. This propagation gives rise to a unidirectional current at the boundary of the support. We use path integrals to define current and unidirectional current, and to provide a direct derivation of the expression for current from the path-integral formulation for both diffusion and quantum mechanics. Furthermore, we give an explicit asymptotic expression for the short-time propagation of an initial wave function with compact support for cases of both a discontinuous derivative and a discontinuous wave function. We show that in the former case the probability propagated across the boundary of the support in time Δt is O(Δt3/2), and the initial unidirectional current is O(Δt1/2). This recovers the Zeno effect for continuous detection of a particle in a given domain. For the latter case the probability propagated across the boundary of the support in time Δt is O(Δt1/2), and the initial unidirectional current is O(Δt-1/2). This is an anti-Zeno effect. However, the probability propagated across a point located at a finite distance from the boundary of the support is O(Δt). This gives a decay law.
We propose a formulation of an absorbing boundary for a quantum particle. The formulation is base... more We propose a formulation of an absorbing boundary for a quantum particle. The formulation is based on a Feynman-type integral over trajectories that are confined by the absorbing boundary. Trajectories that reach the absorbing wall are instantaneously terminated and their probability is discounted from the population of the surviving trajectories. This gives rise to a unidirectional absorption current at the boundary. We calculate the survival probability as a function of time. Several modes of absorption are derived from our formalism: total absorption, absorption that depends on energy levels, and absorption of non-interacting particles. Several applications are given: the slit experiment with an absorbing screen and with absorbing lateral walls, and one dimensional particle between two absorbing walls. The survival probability of a particle between absorbing walls exhibits decay with beats.
We consider the evolution of Green's function of the one-dimensional Schr\"odinger equation in th... more We consider the evolution of Green's function of the one-dimensional Schr\"odinger equation in the presence of the complex potential $-ik\delta(x)$. Our result is the construction of an explicit time-dependent solution which we use to calculate the time-dependent survival probability of a quantum particle. The survival probability decays to zero in finite time, which means that the complex delta potential well is a total absorber for quantum particles. This potential can be interpreted as a killing measure with infinite killing rate concentrated at the origin.
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