17,535 research outputs found
An Experimental Microarchitecture for a Superconducting Quantum Processor
Quantum computers promise to solve certain problems that are intractable for
classical computers, such as factoring large numbers and simulating quantum
systems. To date, research in quantum computer engineering has focused
primarily at opposite ends of the required system stack: devising high-level
programming languages and compilers to describe and optimize quantum
algorithms, and building reliable low-level quantum hardware. Relatively little
attention has been given to using the compiler output to fully control the
operations on experimental quantum processors. Bridging this gap, we propose
and build a prototype of a flexible control microarchitecture supporting
quantum-classical mixed code for a superconducting quantum processor. The
microarchitecture is based on three core elements: (i) a codeword-based event
control scheme, (ii) queue-based precise event timing control, and (iii) a
flexible multilevel instruction decoding mechanism for control. We design a set
of quantum microinstructions that allows flexible control of quantum operations
with precise timing. We demonstrate the microarchitecture and microinstruction
set by performing a standard gate-characterization experiment on a transmon
qubit.Comment: 13 pages including reference. 9 figure
Advances in Quantum Teleportation
Quantum teleportation is one of the most important protocols in quantum
information. By exploiting the physical resource of entanglement, quantum
teleportation serves as a key primitive in a variety of quantum information
tasks and represents an important building block for quantum technologies, with
a pivotal role in the continuing progress of quantum communication, quantum
computing and quantum networks. Here we review the basic theoretical ideas
behind quantum teleportation and its variant protocols. We focus on the main
experiments, together with the technical advantages and disadvantages
associated with the use of the various technologies, from photonic qubits and
optical modes to atomic ensembles, trapped atoms, and solid-state systems.
Analysing the current state-of-the-art, we finish by discussing open issues,
challenges and potential future implementations.Comment: Nature Photonics Review. Comments are welcome. This is a
slightly-expanded arXiv version (14 pages, 5 figure, 1 table
Manipulating a qubit through the backaction of sequential partial measurements and real-time feedback
Quantum measurements not only extract information from a system but also
alter its state. Although the outcome of the measurement is probabilistic, the
backaction imparted on the measured system is accurately described by quantum
theory. Therefore, quantum measurements can be exploited for manipulating
quantum systems without the need for control fields. We demonstrate
measurement-only state manipulation on a nuclear spin qubit in diamond by
adaptive partial measurements. We implement the partial measurement via tunable
correlation with an electron ancilla qubit and subsequent ancilla readout. We
vary the measurement strength to observe controlled wavefunction collapse and
find post-selected quantum weak values. By combining a novel quantum
non-demolition readout on the ancilla with real-time adaption of the
measurement strength we realize steering of the nuclear spin to a target state
by measurements alone. Besides being of fundamental interest, adaptive
measurements can improve metrology applications and are key to
measurement-based quantum computing.Comment: 6 pages, 4 figure
One-way quantum computing with arbitrarily large time-frequency continuous-variable cluster states from a single optical parametric oscillator
One-way quantum computing is experimentally appealing because it requires
only local measurements on an entangled resource called a cluster state.
Record-size, but non-universal, continuous-variable cluster states were
recently demonstrated separately in the time and frequency domains. We propose
to combine these approaches into a scalable architecture in which a single
optical parametric oscillator and simple interferometer entangle up to
( frequencies) (unlimited number of temporal modes) into
a new and computationally universal continuous-variable cluster state. We
introduce a generalized measurement protocol to enable improved computational
performance on this new entanglement resource.Comment: (v4) Consistent with published version; (v3) Fixed typo in arXiv
abstract, 14 pages, 8 figures; (v2) Supplemental material incorporated into
main text, additional explanations added, results unchanged, 14 pages, 8
figures; (v1) 5 pages (3 figures) + 6 pages (5 figures) of supplemental
material; submitted for publicatio
- …