Mircea Trif


Department of Physics
University of Basel
Klingelbergstrasse 82
CH-4056 Basel, Switzerland

email:view address


Short CV

2000 - 2005 Undergraduate studies of Physics, Babes-Bolyai University, Cluj-Napoca, Romania
2005 - 2010 PhD with Prof. Daniel Loss, University of Basel, Switzerland
Since Jan. 2010 Postdoc in the group of Prof. Daniel Loss, University of Basel, Switzerland


Show all abstracts.

1.  Spin electric effects in molecular antiferromagnets
Mircea Trif, Filippo Troiani, Dimitrije Stepanenko, and Daniel Loss.
Phys. Rev. B 82, 045429 (2010); arXiv:1001.3584v1 [cond-mat.mes-hall].

Abstract:Molecular nanomagnets show clear signatures of coherent behavior and have a wide variety of effective low-energy spin Hamiltonians suitable for encoding qubits and implementing spin-based quantum information processing. At the nanoscale, the preferred mechanism for the control of a quantum systems is the application of electric fields, which are strong, can be locally applied, and rapidly switched. In this work, we provide the theoretical tools for identifying molecular nanomagnets suitable for electric control. By group-theoretical symmetry analysis we find that the spin-electric coupling in triangular molecules is governed by the modification of the exchange interaction and is possible even in the absence of spin-orbit coupling. In pentagonal molecules the spin-electric coupling can exist only in the presence of spin-orbit interaction. This kind of coupling is allowed for both s=1∕2 and s=3∕2 spins at the magnetic centers. Within the Hubbard model, we find a relation between the spin-electric coupling and the properties of the chemical bonds in a molecule, suggesting that the best candidates for strong spin-electric coupling are molecules with nearly degenerate bond orbitals. We also investigate the possible experimental signatures of spin-electric coupling in nuclear magnetic resonance and electron spin resonance spectroscopy, as well as in the thermodynamic measurements of magnetization, electric polarization, and specific heat of the molecules.

2.  Spin interactions, relaxation and decoherence in quantum dots
Jan Fischer, Mircea Trif, W. A. Coish, and Daniel Loss.
Solid State Communications 149, 1443 (2009).(arXiv:0903.0527 [cond-mat.mes-hall])

We review recent studies on spin decoherence of electrons and holes in quasi-two-dimensional quantum dots, as well as electron-spin relaxation in nanowire quantum dots. The spins of confined electrons and holes are considered major candidates for the realization of quantum information storage and processing devices, provided that sufficently long coherence and relaxation times can be achieved. The results presented here indicate that this prerequisite might be realized in both electron and hole quantum dots, taking one large step towards quantum computation with spin qubits.

3.  Relaxation of hole spins in quantum dots via two-phonon processes
Mircea Trif, Pascal Simon (Orsay), and Daniel Loss.
Phys. Rev. Lett. 103, 106601 (2009).(arXiv:0902.2457; http://arxiv.org/abs/0902.2457).

We investigate theoretically spin relaxation in heavy hole quantum dots in low external magnetic fields. We demonstrate that two-phonon processes and spin-orbit interaction are experimentally relevant and provide an explanation for the recently observed saturation of the spin relaxation rate in heavy hole quantum dots with vanishing magnetic fields. We propose further experiments to identify the relevant spin relaxation mechanisms in low magnetic fields.

4.  Spin-Electric Coupling in Molecular Magnets
Mircea Trif, Filippo Troiani, Dimitrije Stepanenko, and Daniel Loss.
Phys. Rev. Lett. 101, 217201 (2008). arXiv:0805.1158v1

We study the triangular antiferromagnet Cu$_3$ in external electric fields, using symmetry group arguments and a Hubbard model approach. We identify a spin-electric coupling caused by an interplay between spin exchange, spin-orbit interaction, and the chirality of the underlying spin texture of the molecular magnet. This coupling allows for the electric control of the spin (qubit) states, e.g. by using an STM tip or a microwave cavity. We propose an experimental test for identifying molecular magnets exhibiting spin-electric effects.

5.  Spin dynamics in InAs-nanowire quantum-dots coupled to a transmission line
Mircea Trif, Vitaly N. Golovach, and Daniel Loss.
Phys. Rev. B 77, 045434 (2008); arXiv:0708.2091.

We study theoretically electron spins in nanowire quantum dots placed inside a transmission line resonator. Because of the spin-orbit interaction, the spins couple to the electric component of the resonator electromagnetic field and enable coherent manipulation, storage, and read-out of quantum information in an all-electrical fashion. Coupling between distant quantum-dot spins, in one and the same or different nanowires, can be efficiently performed via the resonator mode either in real time or through virtual processes. For the latter case we derive an effective spin-entangling interaction and suggest means to turn it on and off. We consider both transverse and longitudinal types of nanowire quantum-dots and compare their manipulation timescales against the spin relaxation times. For this, we evaluate the rates for spin relaxation induced by the nanowire vibrations (phonons) and show that, as a result of phonon confinement in the nanowire, this rate is a strongly varying function of the spin operation frequency and thus can be drastically reduced compared to lateral quantum dots in GaAs. Our scheme is a step forward to the formation of hybrid structures where qubits of different nature can be integrated in a single device.

6.  Quantum computing with molecular magnets
Dimitrije Stepanenko, Mircea Trif, and Daniel Loss.
Inorganica Chimica Acta 361 (2008) 3740–3745

We discuss the potential of molecular magnets as the building blocks of a quantum computer. The simplification in the control procedure for the quantum gates in many-spin systems coming from the high symmetry is shown to lead to a relatively simple way to address the spin degrees of freedom in molecular magnets. The advantage of an anisotropic effective spin interaction in memory applications is demonstrated on the example of the Grover quantum search algorithm in a generic easy-axis molecular magnet. Electric control of the coupling between the spins is shown to enable two-qubit quantum gates in polyoxometalates.

7.  Theory of spin qubits in nanostructures
B. Trauzettel, M. Borhani, M. Trif, and D. Loss.
J. Phys. Soc. Jpn., Special Topics: Advances in Spintronics, in press (arXiv:0707.4622)

We review recent advances on the theory of spin qubits in nanostructures. We focus on four selected topics. First, we show how to form spin qubits in the new and promising material graphene. Afterwards, we discuss spin relaxation and decoherence in quantum dots. In particular, we demonstrate how charge fluctations in the surrounding environment cause spin decay via spin--orbit coupling. We then turn to a brief overview of how one can use electron-dipole spin resonance (EDSR) to perform single spin rotations in quantum dots using an oscillating electric field. The final topic we cover is the spin-spin coupling via spin-orbit interaction which is an alternative to the usual spin-spin coupling via the Heisenberg exchange interaction.

8.  Spin-spin coupling in electrostatically coupled quantum dots
Mircea Trif, Vitaly N. Golovach, and Daniel Loss.
Phys. Rev. B 75, 085307 (2007); cond-mat/0608512.

We study the spin-spin coupling between two single-electron quantum dots due to the Coulomb and spin-orbit interactions, in the absence of tunneling between the dots. We find an anisotropic XY spin-spin interaction that is proportional to the Zeeman splitting produced by the external magnetic field. This interaction is studied both in the limit of weak and strong Coulomb repulsion with respect to the level spacing of the dot. The interaction is found to be a non-monotonic function of inter-dot distance $a_0$ and external magnetic field, and, moreover, vanishes for some special values of $a_0$ and/or magnetic field orientation. This mechanism thus provides a new way to generate and tune spin interaction between quantum dots. We propose a scheme to measure this spin-spin interaction based on the spin-relaxation-measurement technique.

9.  Quantum effects in the three-dimensional dilute Bose system at finite temperature: renormalization group approach
M. Crisan, M. Trif, and I. Grosu.
Modern Physics Letters B, Vol. 20, No. 20 (2006) 1267-1274

We consider the influence of temperature on the critical behavior of the weakly interacting three-dimensional Bose system. Using the flow equations of the Renormalization group and a Φ4 model with dynamical critical exponent z = 2, we calculated the critical exponent ν, and the thermodynamic parameters near the critical temperature, taking into consideration the quantum effects. The quantum effects considered in this method gives ν the value 0.75, which is close to the value 0.73 obtained by the polynomial method. The critical temperature shift ΔTc was obtained, in the lowest order approximation, proportional to the scattering length.