Change search
Refine search result
1 - 11 of 11
CiteExportLink to result list
Permanent link
Cite
Citation style
  • apa
  • harvard1
  • ieee
  • modern-language-association-8th-edition
  • vancouver
  • Other style
More styles
Language
  • de-DE
  • en-GB
  • en-US
  • fi-FI
  • nn-NO
  • nn-NB
  • sv-SE
  • Other locale
More languages
Output format
  • html
  • text
  • asciidoc
  • rtf
Rows per page
  • 5
  • 10
  • 20
  • 50
  • 100
  • 250
Sort
  • Standard (Relevance)
  • Author A-Ö
  • Author Ö-A
  • Title A-Ö
  • Title Ö-A
  • Publication type A-Ö
  • Publication type Ö-A
  • Issued (Oldest first)
  • Issued (Newest first)
  • Created (Oldest first)
  • Created (Newest first)
  • Last updated (Oldest first)
  • Last updated (Newest first)
  • Disputation date (earliest first)
  • Disputation date (latest first)
  • Standard (Relevance)
  • Author A-Ö
  • Author Ö-A
  • Title A-Ö
  • Title Ö-A
  • Publication type A-Ö
  • Publication type Ö-A
  • Issued (Oldest first)
  • Issued (Newest first)
  • Created (Oldest first)
  • Created (Newest first)
  • Last updated (Oldest first)
  • Last updated (Newest first)
  • Disputation date (earliest first)
  • Disputation date (latest first)
Select
The maximal number of hits you can export is 250. When you want to export more records please use the Create feeds function.
  • 1. Croke, Sarah
    et al.
    Barnett, Stephen M.
    Stenholm, Stig
    KTH, School of Engineering Sciences (SCI), Physics.
    Linear transformations of quantum states2008In: Annals of Physics, ISSN 0003-4916, E-ISSN 1096-035X, Vol. 323, no 4, p. 893-906Article in journal (Refereed)
    Abstract [en]

    This paper considers the most general linear transformation of a quantum state. We enumerate the conditions necessary to retain a physical interpretation of the transformed state: hermiticity, normalization and complete positivity. We show that these can be formulated in terms of an associated transformation introduced by Choi in 1975. We extend his treatment and display the mathematical argumentation in a manner closer to that used in traditional quantum physics. We contend that our approach displays the implications of the physical requirements in a simple and intuitive way. In addition, defining an arbitrary vector, we may derive a probability distribution over the spectrum of the associated transformation. This fixes the average of the eigenvalue independently of the vector chosen. The formal results are illustrated by a couple of examples.

  • 2.
    Ferreiros, Yago
    et al.
    KTH, School of Engineering Sciences (SCI), Physics.
    Fradkin, Eduardo
    Boson-fermion duality in a gravitational background2018In: Annals of Physics, ISSN 0003-4916, E-ISSN 1096-035X, Vol. 399, no O S, 1990, NUCLEAR PHYSICS B, V346, P293 m Thanh Son, 2015, PHYSICAL REVIEW X, V5, adlyn Barry, 2015, PHYSICAL REVIEW B, V91, omov Andrey, 2015, PHYSICAL REVIEW LETTERS, V114, omov Andrey, 2015, PHYSICAL REVIEW LETTERS, V114, omov Andrey, 2014, PHYSICAL REVIEW LETTERS, V113, o Gil Young, 2014, PHYSICAL REVIEW B, V90,, p. 1-25, article id OVAS DP, 1985, NUCLEAR PHYSICS B, V251, P117Article in journal (Refereed)
    Abstract [en]

    We study the 2+1 dimensional boson-fermion duality in the presence of background curvature and electromagnetic fields. The main players are, on the one hand, a massive complex vertical bar phi vertical bar(4) scalar field coupled to a U(1) Maxwell-Chern-Simons gauge field at level 1, representing a relativistic composite boson with one unit of attached flux, and on the other hand, a massive Dirac fermion. We show that, in a curved background and at the level of the partition function, the relativistic composite boson, in the infinite coupling limit, is dual to a short-range interacting Dirac fermion. The coupling to the gravitational spin connection arises naturally from the spin factors of the Wilson loop in the Chern-Simons theory. A non-minimal coupling to the scalar curvature is included on the bosonic side in order to obtain agreement between partition functions. Although an explicit Lagrangian expression for the fermionic interactions is not obtained, their short-range nature constrains them to be irrelevant, which protects the duality in its strong interpretation as an exact mapping at the IR fixed point between a Wilson-Fisher-Chern-Simons complex scalar and a free Dirac fermion. We also show that, even away from the IR, keeping the vertical bar phi vertical bar(4) term is of key importance as it provides the short-range bosonic interactions necessary to prevent intersections of worldlines in the path integral, thus forbidding unknotting of knots and ensuring preservation of the worldline topologies.

  • 3. Klimov, A. B.
    et al.
    Romero, J. L.
    Björk, Gunnar
    KTH, School of Information and Communication Technology (ICT), Microelectronics and Information Technology, IMIT.
    Sanchez-Soto, L. L.
    Discrete phase-space structure of n-qubit mutually unbiased bases2009In: Annals of Physics, ISSN 0003-4916, E-ISSN 1096-035X, Vol. 324, no 1, p. 53-72Article in journal (Refereed)
    Abstract [en]

    We work out the phase-space structure for a system of n qubits. We replace the field of real numbers that label the axes of the continuous phase space by the finite field GF(2(n)) and investigate the geometrical structures compatible with the notion of unbiasedness. These consist of bundles of discrete curves intersecting only at the origin and satisfying certain additional properties. We provide a simple classification of such curves and study in detail the four- and eight-dimensional cases, analyzing also the effect of local transformations. In this way, we provide a comprehensive phase-space approach to the construction of mutually unbiased bases for n qubits.

  • 4.
    Langmann, Edwin
    KTH, School of Engineering Sciences (SCI), Physics, Mathematical Physics. KTH, School of Engineering Sciences (SCI), Physics, Condensed Matter Theory.
    The Luttinger-Schwinger Model1997In: Annals of Physics, ISSN 0003-4916, E-ISSN 1096-035X, Vol. 253, p. 310-331Article in journal (Refereed)
  • 5. Plimak, L. I.
    et al.
    Stenholm, Stig
    KTH, School of Engineering Sciences (SCI), Physics.
    Causal signal transmission by quantum fields. I: Response of the harmonic oscillator2008In: Annals of Physics, ISSN 0003-4916, E-ISSN 1096-035X, Vol. 323, no 8, p. 1963-1988Article in journal (Refereed)
    Abstract [en]

    It is shown that response properties of a quantum harmonic oscillator are in essence those of a classical oscillator, and that, paradoxical as it may be, these classical properties underlie all quantum dynamical properties of the system. The results are extended to noninteracting bosonic fields, both neutral and charged.

  • 6. Plimak, L. I.
    et al.
    Stenholm, Stig
    KTH, School of Engineering Sciences (SCI), Physics.
    Causal signal transmission by quantum fields. II: Quantum-statistical response of interacting bosons2008In: Annals of Physics, ISSN 0003-4916, E-ISSN 1096-035X, Vol. 323, no 8, p. 1989-2017Article in journal (Refereed)
    Abstract [en]

    We analyse nonperturbatively signal transmission patterns in Green's functions of interacting quantum fields. Quantum field theory is reformulated in terms of the nonlinear quantum-statistical response of the field. This formulation applies equally to interacting relativistic fields and nonrelativistic models. Of crucial importance is that all causality properties to be expected of a response formulation indeed hold. Being by construction equivalent to Schwinger's closed-time-loop formalism, this formulation is also shown to be related naturally to both Kubo's linear response and Glauber's macroscopic photodetection theories, being a unification of the two with generalisation to the nonlinear quantum-statistical response problem. In this paper we introduce response formulation of bosons; response reformulation of fermions will be subject of a separate paper.

  • 7. Plimak, L. I.
    et al.
    Stenholm, Stig
    KTH, School of Engineering Sciences (SCI), Physics.
    Causal signal transmission by quantum fields. III: Coherent response of fermions2009In: Annals of Physics, ISSN 0003-4916, E-ISSN 1096-035X, Vol. 324, no 3, p. 600-636Article in journal (Refereed)
    Abstract [en]

    Structural response properties of fermionic fields are investigated. in the presence of fermions the key technical concept becomes response combination, or R-normal product, of field operators. It generalises the notion of time-normal operator product to response problems. Time-normal products are a special case of R-normal products without inputs; this paper thus also generalises the concept of time-normal ordering to fermions. Explicit causality of R-normal products of arbitrary (bosonic and/or fermionic) field operators is proven, and explicit relations expressing them by conventional Green's functions of quantum field theory are derived.

  • 8. Plimak, L. I.
    et al.
    Stenholm, Stig
    KTH, School of Engineering Sciences (SCI), Physics.
    Causal signal transmission by quantum fields. V: Generalised Keldysh rotations and electromagnetic response of the Dirac sea2012In: Annals of Physics, ISSN 0003-4916, E-ISSN 1096-035X, Vol. 327, no 11, p. 2691-2741Article in journal (Refereed)
    Abstract [en]

    The connection between real-time quantum field theory (RTQFT) [see, e.g., A.Kamenev and A.Levchenko, Adv. Phys. 58 (2009) 197] and phase-space techniques [E.Wolf and L.Mandel, Optical Coherence and Quantum Optics (Cambridge, 1995)] is investigated. The Keldysh rotation that forms the basis of RTQFT is shown to be a phase-space mapping of the quantum system based on the symmetric (Weyl) ordering. Following this observation, we define generalised Keldysh rotations based on the class of operator orderings introduced by Cahill and Glauber [K.E. Cahill, R.J. Glauber, Phys.Rev.177 (1969) 1882]. Each rotation is a phase-space mapping, generalising the corresponding ordering from free to interacting fields. In particular, response transformation [L.I.Plimak, S.Stenholm, Ann.Phys. (N.Y.) 323 (2008) 1989] extends the normal ordering of free-field operators to the time-normal ordering of Heisenbergoperators. Structural properties of the response transformation, such as its association with the nonlinear quantum response problem and the related causality properties, hold for all generalised Keldysh rotations.Furthermore, we argue that response transformation is especially suited for RTQFT formulation of spatial, in particular, relativistic, problems, because it extends cancellation of zero-point fluctuations, characteristic of the normal ordering, to interacting fields. As an example, we consider quantised electromagneticfield in the Dirac sea. In the time-normally-ordered representation, dynamics of the field looks essentially classical (fields radiated by currents), without any contribution from zero-point fluctuations. For comparison, we calculate zero-point fluctuations of the interacting electromagneticfield under orderings other than time-normal. The resulting expression is physically inconsistent: it does not obey the Lorentz condition, nor Maxwell's equations.

  • 9. Plimak, L. I.
    et al.
    Stenholm, Stig
    KTH, School of Engineering Sciences (SCI), Physics.
    Causal signal transmission by quantum fields. VI: The Lorentz condition and Maxwell's equations for fluctuations of the electromagnetic field2013In: Annals of Physics, ISSN 0003-4916, E-ISSN 1096-035X, Vol. 338, p. 207-249Article in journal (Refereed)
    Abstract [en]

    The general structure of electromagnetic interactions in the so-called response representation of quantum electrodynamics(QED)is analysed. A formal solution to the general quantum problem of the electromagnetic fieldinteracting with matter is found. Independently, a formal solution to the corresponding problem in classical stochastic electrodynamics(CSED)is constructed. CSED and QED differ only in the replacement of stochastic averages of c-number fields and currents by time-normal averages of the corresponding Heisenbergoperators. All relations of QED connecting quantum field to quantum current lack Planck's constant, and thus coincide with their counterparts in CSED. In Feynman's terms, one encounters complete disentanglement of the potential and current operators in response picture.

  • 10.
    Stenholm, Stig
    KTH, School of Engineering Sciences (SCI), Physics.
    On entropy production2008In: Annals of Physics, ISSN 0003-4916, E-ISSN 1096-035X, Vol. 323, no 11, p. 2892-2904Article in journal (Refereed)
    Abstract [en]

    We investigate the case of a dynamical system when irreversible time evolution is generated by a nonHermitian superoperator on the states of the system. We introduce a generalized scalar product which can be used to construct a monotonically changing functional of the state, a generalized entropy. This will depend on the level of system dynamics described by the evolution equation. In this paper we consider the special case when the irreversibility derives from imbedding the system of interest into a thermal reservoir. The ensuing time evolution is shown to be compatible both with equilibrium thermodynamics and the entropy production near the final steady state. In particular, Prigogine's principle of minimum entropy production is discussed. Also the limit of zero temperature is considered. We present comments on earlier treatments.

  • 11.
    Stenholm, Stig
    et al.
    KTH, Superseded Departments, Physics.
    Jakob, Matthias
    KTH, Superseded Departments, Physics.
    Time inversion in dynamical systems2004In: Annals of Physics, ISSN 0003-4916, E-ISSN 1096-035X, Vol. 310, no 1, p. 106-126Article in journal (Refereed)
    Abstract [en]

    We consider the case of a dynamical system when the time evolution is generated by a non-hermitian superoperator on the states of the system. Assuming the left and right eigenvectors of this to provide complete basis sets, we propose a generalized scalar product which can be used to construct a monotonically changing functional of the state, a generalized entropy. Combining the time-dependent state with its time-reversed counterpart we can define the operation of time inversion even in this case of irreversible evolution. We require that both the forward and reversed time evolution can be obtained from a generalized action principle, and this demand serves to define the form of the time-reversed state uniquely. The work thus generalizes the quantum treatment from the unitary case to the irreversible one. We present a discussion of the approach and derive some of the direct consequences of our results.

1 - 11 of 11
CiteExportLink to result list
Permanent link
Cite
Citation style
  • apa
  • harvard1
  • ieee
  • modern-language-association-8th-edition
  • vancouver
  • Other style
More styles
Language
  • de-DE
  • en-GB
  • en-US
  • fi-FI
  • nn-NO
  • nn-NB
  • sv-SE
  • Other locale
More languages
Output format
  • html
  • text
  • asciidoc
  • rtf