15 research outputs found
Noisy intermediate-scale quantum computing algorithm for solving an -vertex MaxCut problem with log() qubits
Quantum computers are devices, which allow more efficient solutions of
problems as compared to their classical counterparts. As the timeline to
developing a quantum-error corrected computer is unclear, the quantum computing
community has dedicated much attention to developing algorithms for currently
available noisy intermediate-scale quantum computers (NISQ). Thus far, within
NISQ, optimization problems are one of the most commonly studied and are quite
often tackled with the quantum approximate optimization algorithm (QAOA). This
algorithm is best known for computing graph partitions with a maximal
separation of edges (MaxCut), but can easily calculate other problems related
to graphs. Here, I present a novel quantum optimization algorithm, which uses
exponentially less qubits as compared to the QAOA while requiring a
significantly reduced number of quantum operations to solve the MaxCut problem.
Such an improved performance allowed me to partition graphs with 32 nodes on
publicly available 5 qubit gate-based quantum computers without any
preprocessing such as division of the graph into smaller subgraphs. These
results represent a 40% increase in graph size as compared to state-of-art
experiments on gate-based quantum computers such as Google Sycamore. The
obtained lower bound is 54.9% on the solution for actual hardware benchmarks
and 77.6% on ideal simulators of quantum computers. Furthermore, large-scale
optimization problems represented by graphs of a 128 nodes are tackled with
simulators of quantum computers, again without any predivision into smaller
subproblems and a lower solution bound of 67.9% is achieved. The study
presented here paves way to using powerful genetic optimizer in synergy with
quantum computersComment: 5 pages, 4 figures, 2 tables + Supplementary materia
Exactly solving the Kitaev chain and generating Majorana-zero-modes out of noisy qubits
Majorana-zero-modes (MZMs) were predicted to exist as edge states of a
physical system called the Kitaev chain. MZMs should host particles that are
their own antiparticles and could be used as a basis for a qubit which is
robust-to-noise. However, all attempts to prove their existence gave
inconclusive results. Here, the Kitaev chain is exactly solved with a quantum
computing methodology and properties of MZMs are probed by generating
eigenstates of the Kitev Hamiltonian on 3 noisy qubits of a publicly available
quantum computer. After an ontological elaboration I show that two eigenstates
of the Kitaev Hamiltonian exhibit eight signatures attributed to MZMs. The
results presented here are a most comprehensive set of validations of MZMs ever
conducted in an actual physical system. Furthermore, the findings of this
manuscript are easily reproducible for any user of publicly available quantum
computers, solving another important problem of research with MZMs-the result
reproducibility crisis
Simulating Majorana zero modes on a noisy quantum processor
The simulation of systems of interacting fermions is one of the most
anticipated applications of quantum computers. The most interesting simulations
will require a fault-tolerant quantum computer, and building such a device
remains a long-term goal. However, the capabilities of existing noisy quantum
processors have steadily improved, sparking an interest in running simulations
that, while not necessarily classically intractable, may serve as device
benchmarks and help elucidate the challenges to achieving practical
applications on near-term devices. Systems of non-interacting fermions are
ideally suited to serve these purposes. While they display rich physics and
generate highly entangled states when simulated on a quantum processor, their
classical tractability enables experimental results to be verified even at
large system sizes that would typically defy classical simulation. In this
work, we use a noisy superconducting quantum processor to prepare Majorana zero
modes as eigenstates of the Kitaev chain Hamiltonian, a model of
non-interacting fermions. Our work builds on previous experiments with
non-interacting fermionic systems. Previous work demonstrated error mitigation
techniques applicable to the special case of Slater determinants. Here, we show
how to extend these techniques to the case of general fermionic Gaussian
states, and demonstrate them by preparing Majorana zero modes on systems of up
to 7 qubits.Comment: 12 pages, 6 figure
Entangling Spins in Double Quantum Dots and Majorana Bound States
We study the coupling between a singlet-triplet qubit realized in a double
quantum dot to a topological qubit realized by spatially well-separated
Majorana bound states. We demonstrate that the singlet-triplet qubit can be
leveraged for readout of the topological qubit and for supplementing the gate
operations that cannot be performed by braiding of Majorana bound states.
Furthermore, we extend our setup to a network of singlet-triplet and
topological hybrid qubits that paves the way to scalable fault-tolerant quantum
computing
Open Source Variational Quantum Eigensolver Extension of the Quantum Learning Machine (QLM) for Quantum Chemistry
Quantum Chemistry (QC) is one of the most promising applications of Quantum
Computing. However, present quantum processing units (QPUs) are still subject
to large errors. Therefore, noisy intermediate-scale quantum (NISQ) hardware is
limited in terms of qubits counts and circuit depths. Specific algorithms such
as Variational Quantum Eigensolvers (VQEs) can potentially overcome such
issues. We introduce here a novel open-source QC package, denoted Open-VQE,
providing tools for using and developing chemically-inspired adaptive methods
derived from Unitary Coupled Cluster (UCC). It facilitates the development and
testing of VQE algorithms. It is able to use the Atos Quantum Learning Machine
(QLM), a general quantum programming framework enabling to write, optimize and
simulate quantum computing programs. Along with Open-VQE, we introduce
myQLM-Fermion, a new open-source module (that includes the key QLM ressources
that are important for QC developments (fermionic second quantization tools
etc...). The Open-VQE package extends therefore QLM to QC providing: (i) the
functions to generate the different types of excitations beyond the commonly
used UCCSD ans{\"a}tz;(ii) a new implementation of the "adaptive derivative
assembled pseudo-Trotter method" (ADAPT-VQE), written in simple class structure
python codes. Interoperability with other major quantum programming frameworks
is ensured thanks to myQLM, which allows users to easily build their own code
and execute it on existing QPUs. The combined Open-VQE/myQLM-Fermion quantum
simulator facilitates the implementation, tests and developments of variational
quantum algorithms towards choosing the best compromise to run QC computations
on present quantum computers while offering the possibility to test large
molecules. We provide extensive benchmarks for several molecules associated to
qubit counts ranging from 4 up to 24
Self-controlled growth of highly uniform Ge/Si hut wires for scalable qubit devices
Semiconductor nanowires have been playing a crucial role in the development
of nanoscale devices for the realization of spin qubits, Majorana fermions,
single photon emitters, nanoprocessors, etc. The monolithic growth of
site-controlled nanowires is a prerequisite towards the next generation of
devices that will require addressability and scalability. Here, combining
top-down nanofabrication and bottom-up self-assembly, we report on the growth
of Ge wires on pre-patterned Si (001) substrates with controllable position,
distance, length and structure. This is achieved by a novel growth process
which uses a SiGe strain-relaxation template and can be generalized to other
material combinations. Transport measurements show an electrically tunable
spin-orbit coupling, with a spin-orbit length similar to that of III-V
materials. Also, capacitive coupling between closely spaced wires is observed,
which underlines their potential as a host for implementing two qubit gates.
The reported results open a path towards scalable qubit devices with Si
compatibility