New J. Phys. 16, 075007 (2014)
http://dx.doi.org/10.1088/1367-2630/16/7/075007
Phys. Rev. A 89, 042322 (2014)
http://dx.doi.org/10.1103/PhysRevA.89.042322
We demonstrate that arbitrary time evolutions of many-body quantum systems can be reversed even in cases when only part of the Hamiltonian can be controlled. The reversed dynamics obtained via optimal control—contrary to standard time-reversal procedures—is extremely robust to external sources of noise. We provide a lower bound on the control complexity of a many-body quantum dynamics in terms of the dimension of the manifold supporting it, elucidating the role played by integrability in this context.
Phys. Rev. B 89, 214408 (2014)
http://dx.doi.org/10.1103/PhysRevB.89.214408
We study the crossover from classical to quantum phase transitions at zero temperature within the framework of
Phys. Rev. Lett. 112, 250502 (2014)
http://dx.doi.org/10.1103/PhysRevLett.112.250502
We propose a simple idea for realizing a quantum gate with two fermions in a double well trap via external optical pulses without addressing the atoms individually. The key components of the scheme are Feshbach resonance and Pauli blocking, which decouple unwanted states from the dynamics. As a physical example we study atoms in the presence of a magnetic Feshbach resonance in a nanoplasmonic trap and discuss the constraints on the operation times for realistic parameters, reaching a fidelity above 99.9% within 42 μs, much shorter than existing atomic gate schemes.
New J. Phys. 16, 103015 (2014)
http://dx.doi.org/10.1088/1367-2630/16/10/103015
Nature Communications 5, 4009 (2014)
doi:10.1038/ncomms5009
The Ramsey interferometer is a prime example of precise control at the quantum level. It is usually implemented using internal states of atoms, molecules or ions, for which powerful manipulation procedures are now available. Whether it is possible to control external degrees of freedom of more complex, interacting many-body systems at this level remained an open question. Here we demonstrate a two-pulse Ramsey-type interferometer for non-classical motional states of a Bose–Einstein condensate in an anharmonic trap.
Phys. Rev. B 90, 155426 (2014)
http://dx.doi.org/10.1103/PhysRevB.90.155426
We study the properties of a quantum particle interacting with a one-dimensional structure of equidistant scattering centers. We derive an analytical expression for the dispersion relation and for the Bloch functions in the presence of both even and odd scattering waves within the pseudopotential approximation. This generalizes the well-known solid-state physics textbook result known as the Kronig-Penney model.
Phys. Rev. B 90, 125154 (2014)
http://dx.doi.org/10.1103/PhysRevB.90.125154
We introduce a variational algorithm to simulate quantum many-body states based on a tree tensor network ansatz which releases the isometry constraint usually imposed by the real-space renormalization coarse graining. This additional numerical freedom, combined with the loop-free topology of the tree network, allows one to maximally exploit the internal gauge invariance of tensor networks, ultimately leading to a computationally flexible and efficient algorithm able to treat open and periodic boundary conditions on the same footing.
Phys. Rev. A 91, 062306 (2015)
http://dx.doi.org/10.1103/PhysRevA.91.062306
Optimal control theory is a powerful tool for improving figures of merit in quantum information tasks. Finding the solution to any optimal control problem via numerical optimization depends crucially on the choice of the optimization functional. Here, we derive a functional that targets the full set of two-qubit perfect entanglers, gates capable of creating a maximally entangled state out of some initial product state. The functional depends on easily computable local invariants and unequivocally determines whether a gate is a perfect entangler.
Phys. Rev. A 91, 062307 (2015)
http://dx.doi.org/10.1103/PhysRevA.91.062307
The difficulty of an optimization task in quantum information science depends on the proper mathematical expression of the physical target. Here we demonstrate the power of optimization functionals targeting an arbitrary perfect two-qubit entangler, which allow generation of a maximally entangled state from some initial product state.