摘要:

Superposition principle for spin degrees of freedom is described in terms of density operators only using a formulated composition law of pure-state density operators. Decoherence phenomenon and visibility of the interference pattern are discussed. ©2000 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.1337718

出版商:AIP    

年代:1900

数据来源: AIP

摘要:

A quantum computer is, if realized, the ultimate machine for completely controlling a quantum-mechanical system. This control enables one to prepare any arbitrary state of the Hilbert space and to determine by will its time evolution. From this point of view, the realization of quantum states with unusual symmetries seems to be possible by the use of such quantum information processing devices. On the other hand, symmetry arguments can be used to gain more insight in such a quantum network consisting of identical qubits and they can even further lead to error prevention codes by identifying decoherence free subspaces. By introducing a collective operator description for quantum networks, we show how to describe ensemble systems using a reduced set of parameters. Further we want to point out some connections between quantum computers and symmetry considerations. ©2000 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.1337719

出版商:AIP    

年代:1900

数据来源: AIP

摘要:

Reasonable requirements of (a) physical invariance under particle permutation and (b) physical completeness of state descriptions [1], enable us to deduce a Symmetric Permutation Rule(SPR): that by taking care with our state descriptions, it is always possible to construct state vectors (or wave functions) that are purely symmetric under pure permutation for all particles, regardless of type distinguishability or spin. The conventional exchange antisymmetry for two identical half-integer spin particles is shown to be due to a subtle interdependence in the individual state descriptions arising from an inherent geometrical asymmetry. For three or more such particles, however, antisymmetrization of the state vector for all pairs simultaneously is shown to be impossible and the SPR makes observably different predictions, although the usual pairwise exclusion rules are maintained. The usual caveat of fermion antisymmetrization—that composite integer spin particles (with fermionic constituents) behave only approximately like bosons—is no longer necessary. ©2000 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.1337720

出版商:AIP    

年代:1900

数据来源: AIP

摘要:

I discuss theories of violations of statistics, including intermediate statistics, parastatistics, parons, and quons. I emphasize quons, which allow small violations of statistics. I analyze the quon algebra and its representations, implications of the algebra including the observables allowed by the superselection rule separating inequivalent representations of the symmetric group, the conservation of statistics rules, and the rule for composite systems of quons. I conclude by raising the questions of possible origins of violations of statistics and of the level at which violations should be expected if they exist. ©2000 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.1337721

出版商:AIP    

年代:1900

数据来源: AIP

摘要:

Theq-mutator theory is used to connect the value of1−|q|,the parameter measuring the “difference” between quons and ordinary bosons and fermions, to experiments that test the spin-statistics connection. Such calculations are best carried out using a density matrix formulation because a superselection rule prevents transitions between states associated with different representations of the permutation group. The interpretation of the experimental results, however, in terms of a quantitative limit on1−|q|can be easily misled by the density matrix formulation. As a concrete example, the theory is applied to a spin-statistics test for photons. The formalism is then applied to spin-statistics tests for electrons in atomic helium and for16Onuclei in molecules. Finally, the analysis is used to extend experimental limits on composite systems such as16Onuclei to provide a test of the spin-statistics connection for the constituents of those composite systems (nucleons and quarks in the case of oxygen nuclei). ©2000 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.1337722

出版商:AIP    

年代:1900

数据来源: AIP

摘要:

We start from the viewpoint of quantum canonical transformations, analogues of the usual classical canonical transformations. We show that in the quantum case, such transformations lead naturally to the definition of some important quantum optics states, including the vacuum, coherent states, squeezed vacuum and squeezed states. We then go on to considerquons, operators satisfying deformed versions of the canonical commutation relations. Extending the idea of a canonical transformation todeformedquantum commutators gives quon analogues of these states, quon states. We finally show that this approach provides us with defining relations for some quantum groups. ©2000 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.1337723

出版商:AIP    

年代:1900

数据来源: AIP

摘要:

Thermodynamical properties of a model quon gas are reported. The quons considered are the objects obeying the deformed commutatoraa†−qa†a=1with−1⩽q⩽1.Althoughq=1andq=−1correspond respectively to boson and fermion statistics, it is not trivial to generate a quon gas which interpolates between the boson gas and the fermion gas without Pauli’s exclusion principle. The proposed model, interpolating between the two limits, can realize the Maxwell-Boltzmann limit atq=0and simulate a free anyon gas. Under the restriction−1⩽q⩽1,the gas is deformed but bosonic in nature. It shows the Bose-Einstein condensation even in two dimensions. ©2000 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.1337724

出版商:AIP    

年代:1900

数据来源: AIP

摘要:

The recent discoveries of new forms of quantum statistics require a close look at the under-lying Fock space structure. This exercise becomes all the more important in order to provide a general classification scheme for various forms of statistics, and establish interconnections among them whenever it is possible. We formulate a theory of generalized Fock spaces, which has a three tired structure consisting of Fock space, statistics and algebra. This general formalism unifies various forms of statistics and algebras, which were earlier considered to describe different systems. Besides, the formalism allows us to construct many new kinds of quantum statistics and the associated algebras of creation and destruction operators. Some of these are: orthostatistics, null statistics or statistics of frozen order, quantum group based statistics and its manyavatars, and ‘doubly-infinite’ statistics. The emergence of new forms of quantum statistics for particles interacting with singular potential is also highlighted. ©2000 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.1337725

出版商:AIP    

年代:1900

数据来源: AIP

摘要:

Orthofermi statistics is characterized by an exclusion principle which is more “exclusive” than Pauli’s exclusion principle: an orbital state shall not contain more than one particle, no matter what the spin direction is. The wavefunction is antisymmetric in spatial indices alone with arbitrary symmetry in the spin indices. Orthobose statistics is corresponding Bose analog: the wavefunction is symmetric in spatial indices, with arbitrary symmetry in spin indices. We construct the quantum field theory of particles obeying these new kinds of quantum statistics. Non-relativistic as well as relativistic quantum field theories with interactions are considered. ©2000 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.1337726

出版商:AIP    

年代:1900

数据来源: AIP

摘要:

The recent confirmation of the occurrence of supersymmetry in nuclei is reviewed in light of the spin-statistics connection. ©2000 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.1337727

出版商:AIP    

年代:1900

数据来源: AIP