Quantum Preprints

We introduce the PBS-calculus to represent and reason on quantum computations involving polarising beam splitters (PBS for short). PBS-diagrams can be used to represent various schemes including quantum-controlled computations, which are known to have multiple computational and communication advantages over classically ordered models like quantum circuits. The PBS-calculus is equipped... Read more
Published on: 2020-02-24
Benchmarking numerical methods in quantum chemistry is one of the key opportunities that quantum simulators can offer. Here, we propose an analog simulator for discrete 2D quantum chemistry models based on cold atoms in optical lattices. We first analyze how to simulate simple models, like the discrete versions of H... Read more
Published on: 2020-02-24
The dominant source of decoherence in contemporary frequency-tunable superconducting qubits is 1/$f$ flux noise. To understand its origin and find ways to minimize its impact, we systematically study flux noise amplitudes in more than 50 flux qubits with varied SQUID geometry parameters and compare our results to a microscopic model... Read more
Published on: 2020-02-24
Rare-earth related electron spins in crystalline hosts are unique material systems, as they can potentially provide a direct interface between telecom band photons and long-lived spin quantum bits. Specifically, their optically accessible electron spins in solids interacting with nuclear spins in their environment are valuable quantum memory resources. Detection of... Read more
Published on: 2020-02-24
Bucket brigade quantum RAM (QRAM) circuits were proposed for their advantageous addressing of the memory. Another quality of these circuits is that queries, once the addresses are determined, can be parallelised. State-of-the-art error-corrected formulation of these circuits, however, had to be decomposed into the Clifford+T gate set, and the initial... Read more
Published on: 2020-02-24
The wave function of an atom passed through a diffraction grating acquires a regular space structure and the interaction of another particle with this atom can be thought of as scattering on a 'quantum grating' composed of a single atom. Probing this 'grating' by collisions with charged projectiles reveals interference... Read more
Published on: 2020-02-24
In this paper we will present tha main features of what can be called Schwinger's foundational approach to Quantum Mechanics. The basic ingredients of this formulation are the textit{selective measurements}, whose algebraic composition rules define a mathematical structure called groupoid, which is associated with any physical system. After the introduction... Read more
Published on: 2020-02-24
The secret key rate of a continuous-variable quantum key distribution (CV-QKD) system is limited by excess noise. A key issue typical to all modern CV-QKD systems implemented with a reference or pilot signal and an independent local oscillator is controlling the excess noise generated from the frequency and phase noise... Read more
Published on: 2020-02-24
We propose a criterion to characterize interacting theories in a suitable Wightman framework of relativistic quantum field theories which incorporates a "singularity hypothesis", which has been conjectured for a long time, is supported by renormalization group theory, but has never been formulated mathematically. The (nonperturbative) wave function renormalization $Z$ occurring... Read more
Published on: 2020-02-24
This thesis is focused on the design and analysis of quantum communication protocols. Several schemes for quantum communication have been introduced in the recent past. For example, quantum teleportation, dense coding, quantum key distribution, quantum secure direct communication, etc., have been rigorously studied in the last 2-3 decades. Specifically, a... Read more
Published on: 2020-02-24