arXiv subjects

T. Choi

Publications and source records attributed to T. Choi.

7 recordsLinked to original sources

arXiv2014

Optimal quantum control of multi-mode couplings between trapped ion qubits for scalable entanglement

We demonstrate high fidelity entangling quantum gates within a chain of five trapped ion qubits by optimally shaping optical fields that couple to multiple collective modes of motion. We individually address qubits with segmented optical pulses to construct multipartite entangled states in a programmable way. This approach enables both high fidelity and fast quantum gates that can be scaled to larger qubit registers for quantum computation and simulation.

quant-ph↗

arXiv2013

Beat note stabilization of mode-locked lasers for quantum information processing

We stabilize a chosen radiofrequency beat note between two optical fields derived from the same mode-locked laser pulse train, in order to coherently manipulate quantum information. This scheme does not require access or active stabilization of the laser repetition rate. We implement and characterize this external lock, in the context of two-photon stimulated Raman transitions between the hyperfine ground states of trapped 171-Yb+ quantum bits.

quant-ph↗

arXiv2013

Counting statistics of hole transfer in a p-type GaAs quantum dot with dense excitation spectrum

Low-temperature transport experiments on a p-type GaAs quantum dot capacitively coupled to a quantum point contact are presented. The time-averaged as well as time-resolved detection of charging events of the dot are demonstrated and they are used to extract the tunnelling rates into and out of the quantum dot. The extracted rates exhibit a super-linear enhancement with the bias applied across the dot which is interpreted in terms of a dense spectrum of excited states contributing to the transport, characteristic for heavy hole systems. The full counting statistics of charge transfer events and the effect of back action is studied. The normal cumulants as well as the recently proposed factorial cumulants are calculated and discussed in view of their importance for interacting systems.

cond-mat.mes-hall↗

arXiv2011

Coherent Electron-Phonon Coupling in Tailored Quantum Systems

The coupling between a two-level system and its environment leads to decoherence. Within the context of coherent manipulation of electronic or quasiparticle states in nanostructures, it is crucial to understand the sources of decoherence. Here, we study the effect of electron-phonon coupling in a graphene and an InAs nanowire double quantum dot. Our measurements reveal oscillations of the double quantum dot current periodic in energy detuning between the two levels. These periodic peaks are more pronounced in the nanowire than in graphene, and disappear when the temperature is increased. We attribute the oscillations to an interference effect between two alternative inelastic decay paths involving acoustic phonons present in these materials. This interpretation predicts the oscillations to wash out when temperature is increased, as observed experimentally.

cond-mat.mes-hall↗

arXiv2010

Highly Tunable Hybrid Quantum Dots with Charge Detection

In order to employ solid state quantum dots as qubits, both a high degree of control over the confinement potential as well as sensitive charge detection are essential. We demonstrate that by combining local anodic oxidation with local Schottky-gates, these criteria are nicely fulfilled in the resulting hybrid device. To this end, a quantum dot with adjacent charge detector is defined. After tuning the quantum dot to contain only a single electron, we are able to observe the charge detector signal of the quantum dot state for a wide range of tunnel couplings.

cond-mat.mes-hall↗

arXiv2010

Observation of excited states in a graphene double quantum dot

We study a graphene double quantum dot in different coupling regimes. Despite the strong capacitive coupling between the dots, the tunnel coupling is below the experimental resolution. We observe additional structures inside the finite-bias triangles, part of which can be attributed to electronic excited dot states, while others are probably due to modulations of the transmission of the tunnel barriers connecting the system to source and drain leads.

cond-mat.mes-hall↗

arXiv2008

Incommensurability and atomic structure of c(2x2)N/Cu(100)

We use a scanning tunneling microscope operating in a low temperature, ultrahigh vacuum environment to study the atomic structure of single layer films of Cu2N grown on Cu(100). The c(2x2) lattice of Cu2N is incommensurate, with a lattice constant of 3.72 +/- 0.02 angstrom that is 3% larger than the bare Cu(100) surface. This finding suggests that strain due to lattice mismatch contributes to self assembly in this system. We find that the image contrast on Cu2N islands depends on bias voltage, which reconciles several interpretations in the literature. We assign features in these STM images to the Cu, N and hollow sites in the Cu2N lattice with the aid of co-adsorbed CO molecules. This atomic registry allows us to characterize four different defects on Cu2N, which influence the sticking coefficient and electronic coupling of adsorbates.

cond-mat.mtrl-sci↗