All

We show that one can quantum simulate the dynamics of a Sachdev-Ye-Kitaev
model with $N$ Majorana modes for time $t$ to precision $\epsilon$ with gate
complexity $O(N^{7/2} t + N^{5/2} t \,{\rm polylog}(N/ \epsilon))$. In addition
to scaling sublinearly in the number of Hamiltonian terms, this gate complexity
represents an exponential improvement in $1/\epsilon$ and large polynomial
improvement in $N$ and $t$ over prior state-of-the-art algorithms which scale
as $O(N^{10} t^2 / \epsilon)$. Our approach involves a variant of the

We investigate the band structure of ABCA-tetralayer graphene (ABCA-TTLG)
subjected to an external potential $V$ applied between top and bottom layers.
Using the tight-binding model, including the nearest $t$ and
next-nearest-neighbor $t'$ hopping, low-energy model and two-band approximation
model we study the band structure variation along the lines $\Gamma-M-K-\Gamma$
in the first Brillouin zone, electronic band gap near Dirac point $K$ and
transmission properties, respectively. Our results reveal that ABCA-TTLG

Silicon spin qubits are a promising quantum computing platform offering long
coherence times, small device sizes, and compatibility with industry-backed
device fabrication techniques. In recent years, high fidelity single-qubit and
two-qubit operations have been demonstrated in Si. Here, we demonstrate
coherent spin control in a quadruple quantum dot fabricated using isotopically
enriched 28Si. We tune the ground state charge configuration of the quadruple

We consider a bipartite quantum conductor and analyze fluctuations of heat
quantity in a subsystem as well as self-information associated with the
reduced-density matrix of the subsystem. By exploiting the multi-contour
Keldysh technique, we calculate the R\'enyi entropy, or the information
generating function, subjected to the constraint of the local heat quantity of
the subsystem, from which the probability distribution of conditional
self-information is derived. We present an equality that relates the optimum

We present a tomographic method which requires only $4d-3$ measurement
outcomes to reconstruct \emph{any} pure quantum state of arbitrary dimension
$d$. Using the proposed scheme we have experimentally reconstructed a large
number of pure states of dimension $d=7$, obtaining a mean fidelity of $0.94$.
Moreover, we performed numerical simulations of the reconstruction process,
verifying the feasibility of the method for higher dimensions. In addition, the

Here we prove the existence and uniqueness of solutions of a class of
integral equations describing two Dirac particles in 1+3 dimensions with direct
interactions. This class of integral equations arises naturally as a
relativistic generalization of the integral version of the two-particle
Schr\"odinger equation. Crucial use of a multi-time wave function
$\psi(x_1,x_2)$ with $x_1,x_2 \in \mathbb{R}^4$ is made. A central feature is
the time delay of the interaction. Our main result is an existence and

The Aharanov-Bohm (AB) effect, which predicts that a magnetic field strongly
influences the wave function of an electrically charged particle, is
investigated in a three site system in terms of the quantum control by an
additional dephasing source. The AB effect leads to a non-monotonic dependence
of the steady-state current on the gauge phase associated with the molecular
ring. This dependence is sensitive to site energy, temperature, and dephasing,
and can be explained using the concept of the dark state. Although the phase

Suppressing undesired non-unitary effects in a quantum system is a major
challenge in quantum computation and quantum control. In this scenario, the
investigation of the adiabatic dynamics under decoherence allows for optimal
strategies in adiabatic protocols in the presence of a surrounding environment.
In this work, we address this point by theoretically and experimentally
analyzing the robustness of the adiabatic theorem in open quantum systems. More

The ZX-Calculus is a graphical language for diagrammatic reasoning in quantum
mechanics and quantum information theory. It comes equipped with an equational
presentation. We focus here on a very important property of the language:
completeness, which roughly ensures the equational theory captures all of
quantum mechanics. We first improve on the known-to-be-complete presentation or
the so-called Clifford fragment of the language - a restriction that is not
universal - by adding some axioms. Thanks to a system of back-and-forth

A phenomenological construction of quantum Langevin equations, based on the
physical criteria of (i) the canonical equal-time commutators, (ii) the Kubo
formula, (iii) the virial theorem and (iv) the quantum fluctuation-dissipation
theorem is presented. The case of a single harmonic oscillator coupled to a
large external bath is analysed in detail. This allows to distinguish a
markovian semi-classical approach, due to Bedeaux and Mazur, from a
non-markovian full quantum approach, due to to Ford, Kac and Mazur. The