arXiv subjects
Jeeva Anandan
Publications and source records attributed to Jeeva Anandan.
Model for Entangled States with Spin-Spin Interaction
A system consisting of two neutral spin 1/2 particles is analyzed for two magnetic field perturbations: 1) an inhomogeneous magnetic field over all space, and 2) external fields over a half space containing only one of the particles. The field is chosen to point from one particle to the other, which results in essentially a one-dimensional problem. A number of interesting features are revealed for the first case: the singlet, which has zero potential energy in the unperturbed case, remains unstable in the perturbing field. The spin zero component of the triplet evolves into a bound state with a double well potential, with the possibility of tunneling. Superposition states can be constructed which oscillate between entangled and unentangled states. For the second case, we show that changes in the magnetic field around one particle affect measurements of the spin of the entangled particle not in the magnetic field nonlocally. By using protective measurements, we show it is possible in principle to establish a nonlocal interaction using the two particles, provided the dipole-dipole potential energy does not vanish and is comparable to the potential energy of the particle in the external field.
Action principle formulation for motion of extended bodies in General Relativity
We present an action principle formulation for the study of motion of an extended body in General Relativity in the limit of weak gravitational field. This gives the classical equations of motion for multipole moments of arbitrary order coupling to the gravitational field. In particular, a new force due to the octupole moment is obtained. The action also yields the gravitationally induced phase shifts in quantum interference experiments due to the coupling of all multipole moments.
Quantum Mechanics in a Rotating Frame
The rotating frame is considered in quantum mechanics on the basis of the position dependent boost relating this frame to the non rotating inertial frame. We derive the Sagnac phase shift and the spin coupling with the rotation in the non relativistic limit by a simple treatment. By taking the low energy limit of the Dirac equation with a spin connection, we obtain the Hamiltonian for the rotating frame, which gives rise to all the phase shifts discussed before. Furthermore, we obtain a new phase shift due to the spin-orbit coupling.
Action based approach to the dynamics of extended bodies in General Relativity
We present, for the first time, an action principle that gives the equations of motion of an extended body possessing multipole moments in an external gravitational field, in the weak field limit. From the action, the experimentally observable quantum phase shifts in the wavefunction of an extended object due to the coupling of its multipole moments with the gravitational field are obtained. Also, since the theory may be quantized using the action, the present approach is useful in the interface between general relativity and quantum mechanics.
Laws, Symmetries, and Reality
It is argued that quantum mechanics follows naturally from the assumptions that there are no fundamental causal laws but only probabilities for physical processes that are constrained by symmetries, and reality is relational in the sense that an object is real only in relation to another object that it is interacting with. The first assumption makes it natural to include in the action for a gauge theory all terms that are allowed by the symmetries, enabling cancellation of infinities, with only the terms in the standard model observable at the energies at which we presently do our experiments. In this approach, it is also natural to have an infinite number of fundamental interactions.
Putting a Spin on the Aharonov-Bohm Oscillations
An experiment that shows the modulation of the Aharonov-Bohm oscillations of magneto-resistance in a mesoscopic ring is described. Possible theoretical explanations of this modulation due to the interaction of the electron spin with the magnetic and electric fields are considered.
Causality, Symmetries, and Quantum Mechanics
It is argued that there is no evidence for causality as a metaphysical relation in quantum phenomena. The assumption that there are no causal laws, but only probabilities for physical processes constrained by symmetries, leads naturally to quantum mechanics. In particular, an argument is made for why there are probability amplitudes that are complex numbers, which obey the Born rule for quantum probabilities. This argument generalizes the Feynman path integral formulation of quantum mechanics to include all possible actions that are allowed by symmetries, but only the lowest order terms are observable at the presently accessible energy scales. The notion of relational reality is introduced in order to give physical meaning to probabilities. This appears to give rise to a new interpretation of quantum mechanics.
Non-locality of Quantum Mechanics and the Locality of General Relativity
The conflict between the locality of general relativity, reflected in its space-time description, and the non-locality of quantum mechanics, contained in its Hilbert space description, is discussed. Gauge covariant non-local observables that depend on gauge fields and gravity as well as the wave function are used in order to try to understand and minimize this conflict within the frame-work of these two theories. Applications are made to the Aharonov-Bohm effect and its generalizations to non Abelian gauge fields and gravity.
Some aspects of separability
We present three necessary separability criteria for bipartite mixed states, the violation of each of these conditions is a sufficient condition for entanglement. Some ideas on the issue of finding a necessary and sufficient criterion of separability are also discussed.
Symmetries, Quantum Geometry, and the Fundamental Interactions
A generalized Noether's theorem and the operational determination of a physical geometry in quantum physics are used to motivate a quantum geometry consisting of relations between quantum states that are defined by a universal group. Making these relations dynamical implies the non local effect of the fundamental interactions on the wave function, as in the Aharonov-Bohm effect and its generalizations to non Abelian gauge fields and gravity. The usual space-time geometry is obtained as the classical limit of this quantum geometry using the quantum state space metric.
Quantum Measurement Problem and the Possible Role of the Gravitational Field
The quantum measurement problem and various unsuccessful attempts to resolve it are reviewed. A suggestion by Diosi and Penrose for the half life of the quantum superposition of two Newtonian gravitational fields is generalized to an arbitrary quantum superposition of relativistic, but weak, gravitational fields. The nature of the ``collapse'' process of the wave function is examined.
Global Topology and Local Violation of Discrete Symmetries
Cosmological models that are locally consistent with general relativity and the standard model in which an object transported around the universe undergoes P, C and CP transformations, are constructed. This leads to generalization of the gauge fields that describe electro-weak and strong interactions by enlarging the gauge groups to include anti-unitary transformations. Gedanken experiments show that if all interactions obey Einstein causality then P, C and CP cannot be violated in these models. But another model, which would violate charge superselection rule even for an isolated system, is allowed. It is suggested that the fundamental physical laws must have these discrete symmetries which are broken spontaneously, or they must be non causal.
Resource Letter GPP-1: Geometric Phases in Physics
This Resource Letter provides a guide to the literature on the geometric angles and phases in classical and quantum physics. Journal articles and books are cited for the following topics: anticipations of the geometric phase, foundational derivations and formulations, books and review articles on the subject, and theoretical and experimental elaborations and applications.
Nonadiabatic Geometric Phase in Quaternionic Hilbert Space
We develop the theory of the nonadiabatic geometric phase, in both the Abelian and non-Abelian cases, in quaternionic Hilbert space.
TOPOLOGICAL PHASES AND THEIR DUALITY IN ELECTROMAGNETIC AND GRAVITATIONAL FIELDS
The duality found by Aharonov and Casher for topological phases in the electromagnetic field is generalized to an arbitrary linear interaction. This provides a heuristic principle for obtaining a new solution of the field equations from a known solution. This is applied to the general relativistic Sagnac phase shift due to the gravitational field in the interference of mass or energy around a line source that has angular momentum and the dual phase shift in the interference of a spin around a line mass. These topological phases are treated both in the linearized limit of general relativity and the exact solutions for which the gravitational sources are cosmic strings containing torsion and curvature, which do not have a Newtonian limit.
REMARKS CONCERNING THE GEOMETRIES OF GRAVITY AND GAUGE FIELDS
An important limitation is shown in the analogy between the Aharonov-Bohm effect and the parallel transport on a cone. It illustrates a basic difference between gravity and gauge fields due to the existence of the solder form for the space-time geometry. This difference is further shown by the observability of the gravitational phase for open paths. This reinforces a previous suggestion that the fundamental variables for quantizing the gravitational field are the solder form and the connection, and not the metric.
The Meaning of Protective Measurements
Protective measurements, which we have introduced recently, allow to measure properties of the state of a single quantum system and even the Schrödinger wave itself. These measurements require a protection, sometimes due to an additional procedure and sometimes due to the potential of the system itself. The analysis of the protective measurements is presented and it is argued, contrary to recent claims, that they measure the quantum state and not the protective potential. Some other misunderstandings concerning our proposal are clarified.