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Björk, G. (2018). Information gain when measuring an unknown qubit. European journal of physics, 39(1), Article ID 015403.
Open this publication in new window or tab >>Information gain when measuring an unknown qubit
2018 (English)In: European journal of physics, ISSN 0143-0807, E-ISSN 1361-6404, Vol. 39, no 1, article id 015403Article in journal (Refereed) Published
Abstract [en]

In quantum information the fundamental information-containing system is the qubit. A measurement of a single qubit can at most yield one classical bit. However, a dichotomous measurement of an unknown qubit will yield much less information about the qubit state. We use Bayesian inference to compute how much information one progressively gets by making sucessive, individual measurements on an ensemble of identically prepared qubits. Perhaps surprisingly, even if the measurements are arranged so that each measurement yields one classical bit, that is, the two possible measurement outcomes are a priori equiprobable, it takes almost a handful of measurements before one has gained one bit of information about the gradually concentrated qubit probability density. We also show that by following a strategy that reaps the maximum information per measurement, we are led to a mutually unbiased basis as our measurement bases. This is a pleasing, although not entirely surprising, result.

Place, publisher, year, edition, pages
Institute of Physics Publishing (IOPP), 2018
Keywords
quantum information, quantum measurement, qubit, mutually unbiased basis, Shannon entropy, Bayesian inference
National Category
Atom and Molecular Physics and Optics
Identifiers
urn:nbn:se:kth:diva-220820 (URN)10.1088/1361-6404/aa94e4 (DOI)000418387100002 ()2-s2.0-85040311937 (Scopus ID)
Funder
Linnaeus research environment CADICSSwedish Research Council, 621-2014-5410
Note

QC 20180111

Available from: 2018-01-11 Created: 2018-01-11 Last updated: 2018-01-22Bibliographically approved
Kim, Y., Björk, G. & Kim, Y.-H. (2017). Experimental characterization of quantum polarization of three-photon states. Physical Review A: covering atomic, molecular, and optical physics and quantum information, 96(3), Article ID 033840.
Open this publication in new window or tab >>Experimental characterization of quantum polarization of three-photon states
2017 (English)In: Physical Review A: covering atomic, molecular, and optical physics and quantum information, ISSN 2469-9926, E-ISSN 2469-9934, Vol. 96, no 3, article id 033840Article in journal (Refereed) Published
Abstract [en]

We experimentally investigate various quantum polarization features of three-photon quantum states, including product and entangled states with varying purity. The three-photon quantum states are categorized into six classes based on the rotation symmetry of mean, variance, and skewness of the polarization distribution. The representative three-photon quantum states in each category are prepared from double-pair emission from pulsed spontaneous parametric down-conversion and quantum interferometry. We demonstrate that the three-photon quantum states show interesting quantum polarization properties, such as maximum sum-uncertainty and hidden polarizations.

Place, publisher, year, edition, pages
AMER PHYSICAL SOC, 2017
National Category
Atom and Molecular Physics and Optics
Identifiers
urn:nbn:se:kth:diva-215445 (URN)10.1103/PhysRevA.96.033840 (DOI)000411452500008 ()2-s2.0-85030311963 (Scopus ID)
Note

QC 20171019

Available from: 2017-10-19 Created: 2017-10-19 Last updated: 2017-11-29Bibliographically approved
Jöns, K. D., Stensson, K., Reindl, M., Swillo, M., Huo, Y., Zwiller, V., . . . Björk, G. (2017). Two-photon interference from two blinking quantum emitters. Physical Review B, 96(7), Article ID 075430.
Open this publication in new window or tab >>Two-photon interference from two blinking quantum emitters
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2017 (English)In: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 96, no 7, article id 075430Article in journal (Refereed) Published
Abstract [en]

We investigate the effect of blinking on the two-photon interference measurement from two independent quantum emitters. We find that blinking significantly alters the statistics in the Hong-Ou-Mandel second-order intensity correlation function g((2))(tau) and the outcome of two-photon interference measurements performed with independent quantum emitters. We theoretically demonstrate that the presence of blinking can be experimentally recognized by a deviation from the g(D)((2))(0) = 0.5 value when distinguishable photons from two emitters impinge on a beam splitter. Our findings explain the significant differences between linear losses and blinking for correlation measurements between independent sources and are experimentally verified using a parametric down-conversion photon-pair source. We show that blinking imposes a mandatory cross-check measurement to correctly estimate the degree of indistinguishability of photons emitted by independent quantum emitters.

Place, publisher, year, edition, pages
AMER PHYSICAL SOC, 2017
National Category
Physical Sciences
Identifiers
urn:nbn:se:kth:diva-214329 (URN)10.1103/PhysRevB.96.075430 (DOI)000407993900008 ()
Note

QC 20170914

Available from: 2017-09-14 Created: 2017-09-14 Last updated: 2018-05-17Bibliographically approved
de la Hoz, P., Björk, G., de Guise, H., Klimov, A. B., Leuchs, G. & Sanchez-Soto, L. L. (2015). Classical polarization multipoles: paraxial versus nonparaxial. Physica Scripta, 90(7), Article ID 074030.
Open this publication in new window or tab >>Classical polarization multipoles: paraxial versus nonparaxial
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2015 (English)In: Physica Scripta, ISSN 0031-8949, E-ISSN 1402-4896, Vol. 90, no 7, article id 074030Article in journal (Refereed) Published
Abstract [en]

We discuss the polarization of paraxial and nonparaxial classical light fields by resorting to a multipole expansion of the corresponding polarization matrix. It turns out that only a dipolar term contributes when one considers SU(2) (paraxial) or SU(3) (nonparaxial) as fundamental symmetries. In this latter case, one can alternatively expand in SU(2) multipoles, and then both a dipolar and a quadrupolar component contribute, which explains the richer structure of this nonparaxial instance. These multipoles uniquely determine Wigner functions, in terms of which we examine some intriguing hallmarks arising in this classical scenario.

Keywords
polarisation, multipolar expansion, near fields
National Category
Physical Sciences
Identifiers
urn:nbn:se:kth:diva-172497 (URN)10.1088/0031-8949/90/7/074030 (DOI)000357541800031 ()2-s2.0-84936870964 (Scopus ID)
Funder
The Swedish Foundation for International Cooperation in Research and Higher Education (STINT)Swedish Research CouncilEU, FP7, Seventh Framework ProgrammeWenner-Gren Foundations
Note

QC 20150825

Available from: 2015-08-25 Created: 2015-08-25 Last updated: 2017-12-04Bibliographically approved
Björk, G., Klimov, A. B., de la Hoz, P., Grassl, M., Leuchs, G. & Sanchez-Soto, L. L. (2015). Extremal quantum states and their Majorana constellations. Physical Review A. Atomic, Molecular, and Optical Physics, 92(3), Article ID 031801.
Open this publication in new window or tab >>Extremal quantum states and their Majorana constellations
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2015 (English)In: Physical Review A. Atomic, Molecular, and Optical Physics, ISSN 1050-2947, E-ISSN 1094-1622, Vol. 92, no 3, article id 031801Article in journal (Refereed) Published
Abstract [en]

The characterization of quantum polarization of light requires knowledge of all the moments of the Stokes variables, which are appropriately encoded in the multipole expansion of the density matrix. We look into the cumulative distribution of those multipoles and work out the corresponding extremal pure states. We find that SU(2) coherent states are maximal to any order whereas the converse case of minimal states (which can be seen as the most quantum ones) is investigated for a diverse range of the number of photons. Taking advantage of the Majorana representation, we recast the problem as that of distributing a number of points uniformly over the surface of the Poincare sphere.

National Category
Physical Sciences
Identifiers
urn:nbn:se:kth:diva-173768 (URN)10.1103/PhysRevA.92.031801 (DOI)000360329200001 ()
Funder
Swedish Research Council, 621-2011-4575EU, FP7, Seventh Framework Programme, Q-ESSENCEWenner-Gren Foundations
Note

QC 20150921

Available from: 2015-09-21 Created: 2015-09-18 Last updated: 2017-12-04Bibliographically approved
Andersson, M., Berglind, E. & Björk, G. (2015). Orbital angular momentum modes do not increase the channel capacity in communication links. New Journal of Physics, 17, Article ID 043040.
Open this publication in new window or tab >>Orbital angular momentum modes do not increase the channel capacity in communication links
2015 (English)In: New Journal of Physics, ISSN 1367-2630, E-ISSN 1367-2630, Vol. 17, article id 043040Article in journal (Refereed) Published
Abstract [en]

The orbital momentum of optical or radio waves can be used as a degree of freedom to transmit information. However, mainly for technical reasons, this degree of freedom has not been widely used in communication channels. The question is if this degree of freedom opens up a new, hitherto unused 'communication window' supporting 'an infinite number of channels in a given, fixed bandwidth' in free space communication as has been claimed? We answer this question in the negative by showing that on the fundamental level, the mode density, and thus room for mode multiplexing, is the same for this degree of freedom as for sets of modes lacking angular momentum. In addition we show that modes with angular momentum are unsuitable for broadcasting applications due to excessive crosstalk or a poor signal-to-noise ratio.

Keywords
orbital angular momentum, mode density, spectral efficiency, free-space communication, broadcasting, signal-to-noise ratio, crosstalk
National Category
Physical Sciences
Identifiers
urn:nbn:se:kth:diva-169360 (URN)10.1088/1367-2630/17/4/043040 (DOI)000353939200003 ()
Note

QC 20150612

Available from: 2015-06-12 Created: 2015-06-12 Last updated: 2017-12-04Bibliographically approved
Björk, G., Grassl, M., de la Hoz, P., Leuchs, G. & Sanchez-Soto, L. L. (2015). Stars of the quantum Universe: extremal constellations on the Poincare sphere. Physica Scripta, 90(10), Article ID 108008.
Open this publication in new window or tab >>Stars of the quantum Universe: extremal constellations on the Poincare sphere
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2015 (English)In: Physica Scripta, ISSN 0031-8949, E-ISSN 1402-4896, Vol. 90, no 10, article id 108008Article in journal (Refereed) Published
Abstract [en]

The characterization of the polarization properties of a quantum state requires the knowledge of the joint probability distribution of the Stokes variables. This amounts to assessing all the moments of these variables, which are aptly encoded in a multipole expansion of the density matrix. The cumulative distribution of these multipoles encapsulates in a handy manner the polarization content of the state. We work out the extremal states for that distribution, finding that SU(2) coherent states are maximal to any order, so they are the most polarized allowed by quantum theory. The converse case of pure states minimizing that distribution, which can be seen as the most quantum ones, is investigated for a diverse range of number of photons. Exploiting the Majorana representation, the problem appears to be closely related to distributing a number of points uniformly over the surface of the Poincare sphere.

Place, publisher, year, edition, pages
[Bjork, Gunnar] Royal Inst Technol KTH, Dept Appl Phys, AlbaNova Univ Ctr, SE-10691 Stockholm, Sweden. [Grassl, Markus; Leuchs, Gerd; Sanchez-Soto, Luis L.] Max Planck Inst Phys Lichts, D-91058 Erlangen, Germany. [Grassl, Markus; Leuchs, Gerd; Sanchez-Soto, Luis L.] Univ Erlangen Nurnberg, Inst Opt Informat & Photon, D-91058 Erlangen, Germany. [de la Hoz, Pablo; Sanchez-Soto, Luis L.] Univ Complutense, Fac Fis, Dept Opt, E-28040 Madrid, Spain.: , 2015
Keywords
polarization, quantum optics, fluctuations, anti-coherence, Majorana representation, spherical t-design
National Category
Physical Sciences
Identifiers
urn:nbn:se:kth:diva-176356 (URN)10.1088/0031-8949/90/10/108008 (DOI)000362529800018 ()2-s2.0-84945232236 (Scopus ID)
Note

QC 20151104

Available from: 2015-11-04 Created: 2015-11-03 Last updated: 2017-12-01Bibliographically approved
Björk, G. & Man'ko, M. (2014). 20th Central European Workshop on Quantum Optics Preface. Physica Scripta, T160, 010301
Open this publication in new window or tab >>20th Central European Workshop on Quantum Optics Preface
2014 (English)In: Physica Scripta, ISSN 0031-8949, E-ISSN 1402-4896, Vol. T160, p. 010301-Article in journal, Editorial material (Refereed) Published
National Category
Atom and Molecular Physics and Optics
Identifiers
urn:nbn:se:kth:diva-145601 (URN)10.1088/0031-8949/2014/T160/010301 (DOI)000335224700001 ()2-s2.0-84900565944 (Scopus ID)
Note

QC 20140611

Available from: 2014-06-11 Created: 2014-05-23 Last updated: 2017-12-05Bibliographically approved
Björk, G., de Guise, H., Klimov, A. B., de la Hoz, P. & Sanchez-Soto, L. L. (2014). Classical distinguishability as an operational measure of polarization. Physical Review A. Atomic, Molecular, and Optical Physics, 90(1), 013830
Open this publication in new window or tab >>Classical distinguishability as an operational measure of polarization
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2014 (English)In: Physical Review A. Atomic, Molecular, and Optical Physics, ISSN 1050-2947, E-ISSN 1094-1622, Vol. 90, no 1, p. 013830-Article in journal (Refereed) Published
Abstract [en]

We put forward an operational degree of polarization that can be extended in a natural way to fields whose wave fronts are not necessarily planar. This measure appears as a distance from a state to the set of all of its polarization-transformed counterparts. By using the Hilbert-Schmidt metric, the resulting degree is a sum of two terms: one is the purity of the state and the other can be interpreted as a classical distinguishability, which can be experimentally determined in an interferometric setup. For transverse fields, this reduces to the standard approach, whereas it allows one to get a straight expression for nonparaxial fields.

Keywords
Degree of polarization, Distinguishability, Nonparaxial fields, Transverse field, Mathematical models, Physics
National Category
Atom and Molecular Physics and Optics
Identifiers
urn:nbn:se:kth:diva-149504 (URN)10.1103/PhysRevA.90.013830 (DOI)000339549000003 ()2-s2.0-84905189793 (Scopus ID)
Funder
The Swedish Foundation for International Cooperation in Research and Higher Education (STINT)Swedish Research Council, 621-2011-4575
Note

QC 20140822

Available from: 2014-08-22 Created: 2014-08-22 Last updated: 2017-12-05Bibliographically approved
Stensson, K., Björk, G. & Gallo, K. (2014). Green-pumped parametric downconversion in hexagonally poled MgO:LiTaO3. In: Advanced Solid State Lasers, ASSL 2014: . Paper presented at Advanced Solid State Lasers, ASSL 2014; Hilton Shanghai HongqiaoShanghai; China; November 2014.
Open this publication in new window or tab >>Green-pumped parametric downconversion in hexagonally poled MgO:LiTaO3
2014 (English)In: Advanced Solid State Lasers, ASSL 2014, 2014Conference paper, Published paper (Refereed)
Abstract [en]

We demonstrate multi-beam optical parametric generation in the 800-1550 nm spectral range sustained by concurrent nonlinear processes in hexagonally poled MgO-doped LiTaO<inf>3</inf>. Experiments performed with a nanosecond pump at 532 nm yield good agreement with theoretical predictions and hold promise for novel coherent parametric sources based on 2D nonlinear lattices.

National Category
Other Physics Topics
Identifiers
urn:nbn:se:kth:diva-174742 (URN)2-s2.0-84929018236 (Scopus ID)978-155752822-3 (ISBN)
Conference
Advanced Solid State Lasers, ASSL 2014; Hilton Shanghai HongqiaoShanghai; China; November 2014
Note

QC 20151012

Available from: 2015-10-12 Created: 2015-10-07 Last updated: 2015-10-12Bibliographically approved
Organisations
Identifiers
ORCID iD: ORCID iD iconorcid.org/0000-0002-2082-9583

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