Kee-Su Park - Academia.edu (original) (raw)
Papers by Kee-Su Park
Physics and Applications of Graphene - Theory, Mar 22, 2011
We present the electronic properties of massless Dirac fermions characterized by geometry and top... more We present the electronic properties of massless Dirac fermions characterized by geometry and topology on a graphene sheet in this chapter. Topological effects can be elegantly illuminated by the Atiyah-Singer index theorem. It leads to a topological invariant under deformations on the Dirac operator and plays an essential role in formulating supersymmetric quantum mechanics over twisted Dolbeault complex caused by the topological deformation of the lattice in a graphene system. Making use of the G index theorem and a high degree of symmetry, we study deformed energy eigenvalues in graphene. The Dirac fermion results in SU(4) symmetry as a high degree of symmetry in the noninteracting Hamiltonian of the monolayer graphene. Under the topological deformation the zero-energy states emerge naturally without the Zeeman splitting at the Fermi points in the graphene sheet. In the case of nonzero energy, the up-spin and down-spin states have the exact high symmetries of spin, forming the pseudospin singlet pairing. We describe the peculiar and unconventional quantum Hall effects of the n = 0 Landau level in monolayer graphene on the basis of the G index theorem and the high degree of symmetry.
International Journal of Modern Physics B, 2001
We use a continuous-time path integral to obtain the semiclassical propagator for minimal-spread ... more We use a continuous-time path integral to obtain the semiclassical propagator for minimal-spread spin coherent states. We pay attention to the extra phase. This extra correction of phase is related to an anomaly in the fluctuation determinant. We show that if this extra factor is included, the semiclassical propagator has the correct short time behaviour to O(T2), and demonstrate its consistency under dissection of the path.
Physical Review B, 2006
We investigated decoherence of a Josephson vortex quantum bit ͑qubit͒ in dissipative and noisy en... more We investigated decoherence of a Josephson vortex quantum bit ͑qubit͒ in dissipative and noisy environment. As the Josephson vortex qubit ͑JVQ͒ is fabricated by using a long Josephson junction ͑LJJ͒, we use the perturbed sine-Gordon equation to describe the phase dynamics representing a two-state system and estimate the effects of quasiparticle dissipation and weakly fluctuating critical and bias currents on the relaxation time T 1 and on the dephasing time T. We show that the critical current fluctuation does not contribute to dephasing of the qubit in the lowest order approximation. Modeling the weak current variation from magnetic field fluctuations in the LJJ by using the Gaussian colored noise with long correlation time, we show that the coherence time T 2 is limited by the low frequency current noise at very low temperatures. Also, we show that a ultra-long coherence time may be obtained from the JVQ by using experimentally accessible value of physical parameters.
Physica C: Superconductivity, 2007
We investigated decoherence of a Josephson vortex quantum bit (qubit) in dissipative and noisy en... more We investigated decoherence of a Josephson vortex quantum bit (qubit) in dissipative and noisy environment. As the Josephson vortex qubit (JVQ) is fabricated by using a long Josephson junction (LJJ), we use the perturbed sine-Gordon equation to describe the phase dynamics representing a two-state system and estimate the effects of quasiparticle dissipation and weakly fluctuating critical and bias currents on the relaxation time T1 and on the dephasing time T φ. We show that the critical current fluctuation does not contribute to dephasing of the qubit in the lowest order approximation. Modeling the weak current variation from magnetic field fluctuations in the LJJ by using the Gaussian colored noise with long correlation time, we show that the coherence time T2 is limited by the low frequency current noise at very low temperatures. Also, we show that an ultra-long coherence time may be obtained from the JVQ by using experimentally accessible value of physical parameters.
Journal of Mathematical Physics, 2003
We use an instanton approximation to the continuous-time spin coherentstate path integral to obta... more We use an instanton approximation to the continuous-time spin coherentstate path integral to obtain the tunnel splitting of classically degenerate ground states. We show that provided the fluctuation determinant is carefully evaluated, the path integral expression is accurate to order O(1/j). We apply the method to the LMG model and to the molecular magnet Fe 8 in a transverse field. This paper is dedicated to the memory of Victor Belinicher, who was lost when Siberia Airlines flight 1812 was shot down over the Black Sea, Oct 4th 2001. Victor made many contributions to physics, in particular to the spin tunneling problem.
Journal of Mathematical Physics, 2000
We use a continuous-time path integral to obtain the semiclassical propagator for minimal-spread ... more We use a continuous-time path integral to obtain the semiclassical propagator for minimal-spread spin coherent states. We pay particular attention to the "extra phase" discovered by Solari and Kochetov, and show that this correction is related to an anomaly in the fluctuation determinant. We show that, once this extra factor is included, the semiclassical propagator has the correct short time behaviour to O(T 2), and demonstrate its consistency under dissection of the path.
Physics and Applications of Graphene - Theory, Mar 22, 2011
We present the electronic properties of massless Dirac fermions characterized by geometry and top... more We present the electronic properties of massless Dirac fermions characterized by geometry and topology on a graphene sheet in this chapter. Topological effects can be elegantly illuminated by the Atiyah-Singer index theorem. It leads to a topological invariant under deformations on the Dirac operator and plays an essential role in formulating supersymmetric quantum mechanics over twisted Dolbeault complex caused by the topological deformation of the lattice in a graphene system. Making use of the G index theorem and a high degree of symmetry, we study deformed energy eigenvalues in graphene. The Dirac fermion results in SU(4) symmetry as a high degree of symmetry in the noninteracting Hamiltonian of the monolayer graphene. Under the topological deformation the zero-energy states emerge naturally without the Zeeman splitting at the Fermi points in the graphene sheet. In the case of nonzero energy, the up-spin and down-spin states have the exact high symmetries of spin, forming the pseudospin singlet pairing. We describe the peculiar and unconventional quantum Hall effects of the n = 0 Landau level in monolayer graphene on the basis of the G index theorem and the high degree of symmetry.
International Journal of Modern Physics B, 2001
We use a continuous-time path integral to obtain the semiclassical propagator for minimal-spread ... more We use a continuous-time path integral to obtain the semiclassical propagator for minimal-spread spin coherent states. We pay attention to the extra phase. This extra correction of phase is related to an anomaly in the fluctuation determinant. We show that if this extra factor is included, the semiclassical propagator has the correct short time behaviour to O(T2), and demonstrate its consistency under dissection of the path.
Physical Review B, 2006
We investigated decoherence of a Josephson vortex quantum bit ͑qubit͒ in dissipative and noisy en... more We investigated decoherence of a Josephson vortex quantum bit ͑qubit͒ in dissipative and noisy environment. As the Josephson vortex qubit ͑JVQ͒ is fabricated by using a long Josephson junction ͑LJJ͒, we use the perturbed sine-Gordon equation to describe the phase dynamics representing a two-state system and estimate the effects of quasiparticle dissipation and weakly fluctuating critical and bias currents on the relaxation time T 1 and on the dephasing time T. We show that the critical current fluctuation does not contribute to dephasing of the qubit in the lowest order approximation. Modeling the weak current variation from magnetic field fluctuations in the LJJ by using the Gaussian colored noise with long correlation time, we show that the coherence time T 2 is limited by the low frequency current noise at very low temperatures. Also, we show that a ultra-long coherence time may be obtained from the JVQ by using experimentally accessible value of physical parameters.
Physica C: Superconductivity, 2007
We investigated decoherence of a Josephson vortex quantum bit (qubit) in dissipative and noisy en... more We investigated decoherence of a Josephson vortex quantum bit (qubit) in dissipative and noisy environment. As the Josephson vortex qubit (JVQ) is fabricated by using a long Josephson junction (LJJ), we use the perturbed sine-Gordon equation to describe the phase dynamics representing a two-state system and estimate the effects of quasiparticle dissipation and weakly fluctuating critical and bias currents on the relaxation time T1 and on the dephasing time T φ. We show that the critical current fluctuation does not contribute to dephasing of the qubit in the lowest order approximation. Modeling the weak current variation from magnetic field fluctuations in the LJJ by using the Gaussian colored noise with long correlation time, we show that the coherence time T2 is limited by the low frequency current noise at very low temperatures. Also, we show that an ultra-long coherence time may be obtained from the JVQ by using experimentally accessible value of physical parameters.
Journal of Mathematical Physics, 2003
We use an instanton approximation to the continuous-time spin coherentstate path integral to obta... more We use an instanton approximation to the continuous-time spin coherentstate path integral to obtain the tunnel splitting of classically degenerate ground states. We show that provided the fluctuation determinant is carefully evaluated, the path integral expression is accurate to order O(1/j). We apply the method to the LMG model and to the molecular magnet Fe 8 in a transverse field. This paper is dedicated to the memory of Victor Belinicher, who was lost when Siberia Airlines flight 1812 was shot down over the Black Sea, Oct 4th 2001. Victor made many contributions to physics, in particular to the spin tunneling problem.
Journal of Mathematical Physics, 2000
We use a continuous-time path integral to obtain the semiclassical propagator for minimal-spread ... more We use a continuous-time path integral to obtain the semiclassical propagator for minimal-spread spin coherent states. We pay particular attention to the "extra phase" discovered by Solari and Kochetov, and show that this correction is related to an anomaly in the fluctuation determinant. We show that, once this extra factor is included, the semiclassical propagator has the correct short time behaviour to O(T 2), and demonstrate its consistency under dissection of the path.