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Geometric momentum for a particle constrained on a curved hypersurface  [PDF]
Q. H. Liu
Mathematics , 2013, DOI: 10.1063/1.4854075
Abstract: A strengthened canonical quantization scheme for the constrained motion on a curved hypersurface is proposed with introduction of the second category of fundamental commutation relations between Hamiltonian and positions/momenta, whereas those between positions and moments are categorized into the first. As an $N-1$ ($N\geq2$) dimensional hypersurface is embedded in an N dimensional Euclidean space, we obtain the proper momentum that depends on the mean curvature. For the surface is the spherical one, a long-standing problem on the form of the geometric potential is resolved in a lucid and unambiguous manner, which turns out to be identical to that given by the so-called confining potential technique. In addition, a new dynamical group SO(N,1) symmetry for the motion on the sphere is demonstrated.
Quantum particle constrained to a curved surface in the presence of a vector potential  [PDF]
M. Encinosa,Ray N. O'Neal, Jr.
Physics , 1999,
Abstract: The Schrodinger equation for a charged particle constrained to a curved surface in the presence of a vector potential is derived using the method of forms. In the limit that the particle is brought infinitesimally close to the surface, a term arises that couples the component of the vector potential normal to the surface to the mean curvature of the surface.
On the geometric potential derived from Hermitian momenta on a curved surface  [PDF]
M. Encinosa
Physics , 2005,
Abstract: A geometric potential $V_C$ depending on the mean and Gaussian curvatures of a surface $\Sigma$ arises when confining a particle initially in a three-dimensional space $\Omega$ onto $\Sigma$ when the particle Hamiltonian $H_\Omega$ is taken proportional to the Laplacian $L$ on $\Omega$. In this work rather than assume $H_\Omega \propto L$, momenta $P_\eta$ Hermitian over $\Omega$ are constructed and used to derive an alternate Hamiltonian $H_\eta$. The procedure leading to $V_C$, when performed with $H_\eta$, is shown to yield $V_C = 0$. To obtain a measure of the difference between the two approaches, numerical results are presented for a toroidal model.
Geometric Momentum: the Proper Momentum for a Free Particle on a Two-dimensional Sphere  [PDF]
Q. H. Liu,L. H. Tang,D. M. Xun
Physics , 2011, DOI: 10.1103/PhysRevA.84.042101
Abstract: In Dirac's canonical quantization theory on systems with second-class constraints, the commutators between the position, momentum and Hamiltonian form a set of algebraic relations that are fundamental in construction of both the quantum momentum and the Hamiltonian. For a free particle on a two-dimensional sphere or a spherical top, results show that the well-known canonical momentum p_{{\theta}} breaks one of the relations, while three components of the momentum expressed in the three-dimensional Cartesian system of axes as p_{i} (i=1,2,3) are satisfactory all around. This momentum is not only geometrically invariant but also self-adjoint, and we call it geometric momentum. The nontrivial commutators between p_{i} generate three components of the orbital angular momentum; thus the geometric momentum is fundamental to the angular one. We note that there are five different forms of the geometric momentum proposed in the current literature, but only one of them turns out to be meaningful.
The point of departure of a particle sliding on a curved surface  [PDF]
Amir Aghamohammadi
Physics , 2012, DOI: 10.1088/0143-0807/33/5/1111
Abstract: A particle is thrown tangentially on a surface. It is shown that for some surfaces and for special initial velocities the thrown particle leaves immediately the surface, and for special conditions it never leaves the surface. The conditions for leaving the surface is investigated. The problem is studied for a surface with the cross section $y=f(x)$. The surfaces with the equations $f(x)= -\alpha x^{k}\ (\alpha, k>0)$ is considered in more detail. At the end the effect of friction is also considered.
Momentum spectrometry of spherical harmonics and a probe of geometric embedding effect  [PDF]
Q. H. Liu
Physics , 2012,
Abstract: As a submanifold is embedded into higher dimensional flat space, quantum mechanics gives various embedding quantities, e.g., the geometric momentum and geometric potential, etc. For a particle moving on a two-dimensional sphere or a free rotation of a spherical top, the projections of the geometric momentum p and the angular momentum L onto a certain Cartesian axis form a complete set of commuting observables as [p_{i},L_{i}]=0 (i=1,2,3). We have therefore a (p_{i},L_{i}) representation for the states on the two-dimensional spherical surface. The geometric momentum distribution of the ground states for a freely rotating rigid rotor seems within the resolution power of present momentum spectrometer and can be measured to probe the embedding effect.
How the Geometric Calculus Resolves the Ordering Ambiguity of Quantum Theory in Curved Space  [PDF]
Matej Pavsic
Physics , 2001, DOI: 10.1088/0264-9381/20/13/318
Abstract: The long standing problem of the ordering ambiguity in the definition of the Hamilton operator for a point particle in curved space is naturally resolved by using the powerful geometric calculus based on Clifford Algebra. The momentum operator is defined to be the vector derivative (the gradient) multiplied by $-i$; it can be expanded in terms of basis vectors $\gamma_\mu$ as $p = -i \gamma^\mu \p_\mu$. The product of two such operators is unambiguous, and such is the Hamiltonian which is just the D'Alambert operator in curved space; the curvature scalar term is not present in the Hamiltonian if we confine our consideration to scalar wave functions only. It is also shown that $p$ is Hermitian and self-adjoint operator: the presence of the basis vectors $\gamma^\mu$ compensates the presence of $\sqrt{|g|}$ in the matrix elements and in the scalar product. The expectation value of such operator follows the classical geodetic line.
Quantum motion of a point particle in the presence of the Aharonov--Bohm potential in curved space  [PDF]
Edilberto O. Silva,Sérgio C. Ulhoa,Fabiano M. Andrade,Cleverson Filgueiras,R. G. G. Amorin
Physics , 2015, DOI: 10.1016/j.aop.2015.09.011
Abstract: The nonrelativistic quantum dynamics of a spinless charged particle in the presence of the Aharonov--Bohm potential in curved space is considered. We chose the surface as being a cone defined by a line element in polar coordinates. The geometry of this line element establishes that the motion of the particle can occur on the surface of a cone or an anti--cone. As a consequence of the nontrivial topology of the cone and also because of two--dimensional confinement, the geometric potential should be taken into account. At first, we establish the conditions for the particle describing a circular path in such a context. Because of the presence of the geometric potential, which contains a singular term, we use the self--adjoint extension method in order to describe the dynamics in all space including the singularity. Expressions are obtained for the bound state energies and wave functions.
Quantum mechanics on curved 2D systems with electric and magnetic fields  [PDF]
Giulio Ferrari,Giampaolo Cuoghi
Physics , 2008, DOI: 10.1103/PhysRevLett.100.230403
Abstract: We derive the Schroedinger equation for a spinless charged particle constrained to a curved surface with electric and magnetics fields applied. The particle is confined on the surface using a thin-layer procedure, giving rise to the well-known geometric potential. The electric and magnetic fields are included via the four-potential. We find that there is no coupling between the fields and the surface curvature and that, with a proper choice of the gauge, the surface and transverse dynamics are exactly separable. Finally, the Hamiltonian for the cylinder, sphere and torus are analytically derived.
Geometric momentum in the Monge parametrization of two dimensional sphere  [PDF]
D. M. Xun,Q. H. Liu
Physics , 2012,
Abstract: A two dimensional surface can be considered as three dimensional shell whose thickness is negligible in comparison with the dimension of the whole system. The quantum mechanics on surface can be first formulated in the bulk and the limit of vanishing thickness is then taken. The gradient operator and the Laplace operator originally defined in bulk converges to the geometric ones on the surface, and the so-called geometric momentum and geometric potential are obtained. On the surface of two dimensional sphere the geometric momentum in the Monge parametrization is explicitly explored. Dirac's theory on second-class constrained motion is resorted to for accounting for the commutator [x_{i},p_{j}]=i \hbar({\delta}_{ij}-x_{i}x_{j}/r^2) rather than [x_{i},p_{j}]=i\hbar{\delta}_{ij} that does not hold true any more. This geometric momentum is geometric invariant under parameters transformation, and self-adjoint.
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