More details on the work in the following poster (and more!) can be found at arXiv:1707.07482

### Neutralising the dark side of quantum networks

T. P. Le^{*,‡} & S. Severini^{†}

^{*} EPSRC Centre for Doctoral Training (CDT) in Delivering Quantum Technologies, University College London

^{†} Department of Computer Science, University College London

^{‡} thao.le.16@ucl.ac.uk

#### //Brief

**//dark subspace** the vector subspace orthogonal to the target node (a.k.a. invariant^{1}/ orthogonal^{2}/ trapping-free^{2} subspace)

**//identify** spanned by all eigenvectors with a zero at the target-node position

**//task** neutralise the dark subspace to enhance quantum transport

**//results**^{3}

- given an underlying network, there exists a Hamiltonian with node interactions such that there is no dark subspace
- very large graphs asymptotically almost surely have no dark subspace

#### //Tactic 01 - Avoid

**//what** initialise completely outside the dark subspace^{4}

**//why** zero component stuck in the dark subspace; entire transfer possible

**//requires** initial superpositions/delocalised state

#### //Tactic 02 - Control

**//what** time-varying control fields change the dynamics on the network

**//why** disrupts the dark subspace and evolves the state towards the target

**//see also** controllability^{5}

#### //Tactic 03 - Disrupt

**//what** local static noise, local dephasing, dissipation on the network^{1,2}

**//why** changes eigenspectrum and decreases/destroys the dark subspace

**//see also** environment-assisted transport

##### References

- Caruso et al, J. Chem. Phys. 131, 105106 (2009)
- Wu et al, Phys. Rev. Lett. 110, (2013)
- Le & Severini, in preparation (2017)
- Schijven & Mülken, Phys. Rev. E 85, (2012)
- Pemberton-Ross & Schirmer, Phys. Rev. A 82, (2010)

##### Other

- DQT Logo
- poster by TPLE 2017