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We regret to inform you that due to COVID-19 spread and frozen mobility
were forced to CANCEL
the workshop. Thank you for your understanding
and looking forward to see you at CEQIP 202+.
Area-law-like systems with entangled states can preserve ergodicity
We study the ground entangled state of the one-dimensional spin-1/2 Ising ferromagnet at its transverse-field critical point. When this problem is expressed in terms of independent fermions, we show that the usual thermostatistical sums emerging within Fermi-Dirac statistics can, for an L-sized subsystem, be indistinctively taken up to L terms or up to lnL terms, providing a neat understanding of the origin of the logarithmic scaling of the entanglement entropy in the system. This is interpreted as a compact occupancy of the phase-space of the L-subsystem, hence standard Boltzmann-Gibbs thermodynamics quantities with an effective system size V ≈ ln(L) are appropriate and are explicitly calculated. The calculations are then to be done in a Hilbert space whose effective dimension is 2ln(L) instead of 2L. In this we can assume ergodicity. Our analysis suggests a scenario where the physical systems are essentially grouped into three classes, in terms of their phase-space occupancy, ergodicity and Lebesgue measure.
Andre M. C. Souza, Peter Rapčan and Constantino Tsallis
The European Physical Journal Special Topics 229, 759–772 (2020)
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Coherence of a Driven Electron Spin Qubit Actively Decoupled from Quasistatic Noise
The coherence of electron spin qubits in semiconductor quantum dots suffers mostly from low-frequency noise. During the past decade, efforts have been devoted to mitigate such noise by material engineering, leading to substantial enhancement of the spin dephasing time for an idling qubit. However, the role of the environmental noise during spin manipulation, which determines the control fidelity, is less understood. We demonstrate an electron spin qubit whose coherence in the driven evolution is limited by high-frequency charge noise rather than the quasistatic noise inherent to any semiconductor device. We employ a feedback-control technique to actively suppress the latter, demonstrating a π-flip gate fidelity as high as 99.04±0.23% in a gallium arsenide quantum dot. We show that the driven-evolution coherence is limited by the longitudinal noise at the Rabi frequency, whose spectrum resembles the 1/f noise observed in isotopically purified silicon qubits.
Takashi Nakajima, Akito Noiri, Kento Kawasaki, Jun Yoneda, Peter Stano, Shinichi Amaha, Tomohiro Otsuka, Kenta Takeda, Matthieu R. Delbecq, Giles Allison, Arne Ludwig, Andreas D. Wieck, Daniel Loss, and Seigo Tarucha
Phys. Rev. X 10, 011060 (2020)
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11.02.2019 Job opening
PhD positions available
Interested to join our research team for four years of you life? That is
exactly the time the PhD study takes. Currently, we have open several
PhD positions in our Institute. We are open for submissions until
the positions are filled (latest 05/03/2020) with PhD starting
in September 2020. If interested, as the first step, please get
in contact with a potential PhD advisor
(send them your cv, motivation letter and contact to someone
who may write a recommendation letter), discuss the subject
and follow his/her instructions. Do not wait until submission deadline
and do this as soon as possible, because the number of positions
01.02.2020 Job opening
Postdoc position 20.20
We are opening a postdoc position
in the area of theoretical quantum information theory. The postdoc
is expected to work in close collaboration with core members of RCQI
on topics of their common interests (quantum communication,
quantum complexity theory, quantum simulations,
quantum foundations, etc.). Basic gross salary is 1400 eur / month,
however, additional funds, depending on the focus and performance,
are expected. The position is offered for one year, but there is
a possibility for one-year extension. The position
is funded by Institute of Physics of Slovak Academy of Sciences.
The application consists of CV (including list of publications), research statement (short summary of personal research interests and plans), and three names of potential referees we might ask for recommendation. Please send all this information to Michal Sedlak by email (email@example.com) before March 2nd. Only complete applications are considered.
Three kings conference / Trojkáľová konferencia
Annual one day meeting of Czech and Slovak physicists will be held on
January 10th in QUTE Auditorium (RCQI, Institute of Physics
of Slovak Academy of Sciences) in Bratislava. More information and registration form are available
on the meeting website http://quantum.physics.sk/conf/3kk2020.
Influence of applied electric and magnetic fields on a thermally-induced reentrance of a coupled spin-electron model on a decorated square lattice
The combination of an exact and Corner Transfer Matrix Renormalization Group (CTMRG) methods is used to study an influence of external electric and magnetic fields on existence of intriguing reentrant magnetic transitions in a coupled spin-electron model on a decorated square lattice. The two-dimensional (2D) decorated square lattice with localized nodal spins and delocalized electrons is taken into account. It was found that the competition among all involved interactions (the electron hopping, spin-spin and spin-electron interaction, external electric and magnetic fields) in combination with thermal fluctuations can produce new type of reentrant magnetic transitions. Depending on the model parameters the non-zero fields can stabilize or destabilize magnetic reentrance. In addition, an alternative and more effective way, for modulating the magnetic reentrance is found. An origin of intriguing low-temperature round maximum in the specific heat was explained as a consequence of rapid changes in the sublattice magnetizations, which is induced through a competition of all presented interactions.
Hana Čenčariková, Jozef Strečka, Andrej Gendiar
Physica E 115, 113717 (2020)
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