31 research outputs found
Temporally and spectrally multiplexed single photon source using quantum feedback control for scalable photonic quantum technologies
Current proposals for scalable photonic quantum technologies require
on-demand sources of indistinguishable single photons with very high efficiency
(having unheralded loss below ). Even with recent progress in the field
there is still a significant gap between the requirements and state of the art
performance. Here, we propose an on-chip source of multiplexed, heralded
photons. Using quantum feedback control on a photon storage cavity with an
optimized driving protocol, we estimate an on-demand efficiency of and
unheralded loss of order , assuming high efficiency detectors and
intrinsic cavity quality factors of order . We further explain how
temporal- and frequency-multiplexing can be used in parallel to significantly
reduce device requirements if single photon frequency conversion is possible
with efficiency in the same range of
Percolation based architecture for cluster state creation using photon-mediated entanglement between atomic memories
A central challenge for many quantum technologies concerns the generation of
large entangled states of individually addressable quantum memories. Here, we
show that percolation theory allows the rapid production of arbitrarily large
graph states by heralded photonic entanglement in a lattice of atomic memories.
This approach can greatly reduce the time required to produce large cluster
resource states for quantum information processing, including states required
for universal one-way quantum computing. This reduction puts our architecture
in an operational regime where demonstrated collection, coupling and detection
efficiencies are sufficient for generating resource states for universal
quantum computing within an experimentally demonstrated coherence time. The
approach also dispenses the need for time consuming feed-forward,
high-cooperativity interfaces and ancilla single photons, and can also tolerate
a high rate of site imperfections. We also derive the minimum coherence time
for the atomic memory to scalably create large-scale photonic-entanglement
without feed-forward as a function of collection efficiency, setting a critical
benchmark for future experimental demonstrations. We also propose a variant of
the architecture with long-range connections that makes our architecture even
more resilient to low site yields. We analyze our architecture for
nitrogen-vacancy (NV) centers in diamond, though the approach applies to any
atomic or atom-like system.Comment: Supplementary information is available as an ancillary fil
Entanglement generation in a quantum network at distance-independent rate
We develop a protocol for entanglement generation in the quantum internet
that allows a repeater node to use -qubit Greenberger-Horne-Zeilinger (GHZ)
projective measurements that can fuse successfully-entangled {\em links},
i.e., two-qubit entangled Bell pairs shared across network edges, incident
at that node. Implementing -fusion, for , is in principle not much
harder than -fusions (Bell-basis measurements) in solid-state qubit
memories. If we allow even -fusions at the nodes, we find---by developing a
connection to a modified version of the site-bond percolation problem---that
despite lossy (hence probabilistic) link-level entanglement generation, and
probabilistic success of the fusion measurements at nodes, one can generate
entanglement between end parties Alice and Bob at a rate that stays constant as
the distance between them increases. We prove that this powerful network
property is not possible to attain with any quantum networking protocol built
with Bell measurements and multiplexing alone. We also design a two-party
quantum key distribution protocol that converts the entangled states shared
between two nodes into a shared secret, at a key generation rate that is
independent of the distance between the two parties
Architectures for photon-mediated quantum information processing
Thesis: Ph. D., Massachusetts Institute of Technology, Department of Electrical Engineering and Computer Science, 2018.Cataloged from PDF version of thesis.Includes bibliographical references (pages 173-186).In this thesis, I present architectures for quantum information processing where photons are used as the quantum bit (qubit) or for mediating entanglement between other qubits. The emphasis of this research is to simplify the basic building blocks required in such processors. The all-photonic repeater and computing architectures do not require material nonlinearities, and their resource requirements are reduced by several orders of magnitude. The photon-mediated atomic memory architecture is designed to work with faulty memories and experimentally demonstrated values of coherence time and photonic coupling efficiency. In the quantum network architecture, the only operation at every node is probabilistic Bell measurement.by Mihir Pant.Ph. D
High-dimensional unitary transformations and boson sampling on temporal modes using dispersive optics
A major challenge for postclassical boson sampling experiments is the need for a large number of coupled optical modes, detectors, and single-photon sources. Here we show that these requirements can be greatly eased by time-bin encoding and dispersive optics-based unitary transformations. Detecting consecutively heralded photons after time-independent dispersion performs boson sampling from unitaries for which an efficient classical algorithm is lacking. We also show that time-dependent dispersion can implement general single-particle unitary operations. More generally, this scheme promises an efficient architecture for a range of other linear optics experiments.United States. Air Force Office of Scientific Research. Multidisciplinary University Research Initiative (Grant FA9550-14-1-0052
Fault-tolerant Post-Selection for Low Overhead Magic State Preparation
We introduce a framework for fault-tolerant post-selection (FTPS) of
fault-tolerant codes and channels -- such as those based on surface-codes --
using soft-information metrics based on visible syndrome and erasure
information. We introduce several metrics for ranking configurations of
syndromes and erasures. In particular, we introduce the \emph{logical gap} (and
variants thereof) as a powerful soft-information metric for predicting logical
error rates of fault-tolerant channels based on topological error-correcting
codes. The logical gap is roughly the unsigned weight difference between
inequivalent logical corrections and is adaptable to any tailored noise model
or decoder. We deploy this framework to prepare high-quality surface code magic
states with low overhead under a model of independent and identically
distributed (\emph{i.i.d.}) Pauli and erasure errors. Post-selection strategies
based on the logical gap can suppress the encoding error rate of a magic state
preparation channel to the level of the physical error rate with low overhead.
For example, when operating at the bulk threshold of the corresponding
surface code, an overall reduction of the encoding error rate by a factor of
is achievable with a relative overhead factor of (approximately
times less than that of simple syndrome-counting rules). We analyze a
schematic buffer architecture for implementing post-selection rules on magic
state factories in the context of magic state distillation. The FTPS framework
can be utilized for mitigating errors in more general fault-tolerant logical
channels.Comment: 10+7 pages, 13 figures, comments welcom
Single Photon Detection by Cavity-Assisted All-Optical Gain
We consider the free carrier dispersion effect in a semiconductor nanocavity
in the limit of discrete photoexcited electron-hole pairs. This analysis
reveals the possibility of ultrafast, incoherent transduction and gain from a
single photon signal to a strong coherent probe field. Homodyne detection of
the displaced probe field enables a new method for room temperature,
photon-number-resolving single photon detection. In particular, we estimate
that a single photon absorbed within a silicon nanocavity can, within tens of
picoseconds, be detected with efficiency and a dark count rate on
the order of kHz assuming a mode volume for a 4.5 micron probe wavelength and a loaded
quality factor on the order of .Comment: 7 pages, 3 figures, 1 table (main text); 14 pages, 12 figures
(supplementary
Increasing error tolerance in quantum computers with dynamic bias arrangement
Many quantum operations are expected to exhibit bias in the structure of
their errors. Recent works have shown that a fixed bias can be exploited to
improve error tolerance by statically arranging the errors in beneficial
configurations. In some cases an error bias can be dynamically reconfigurable,
an example being linear optical fusion where the basis of a fusion failure can
be chosen before the measurement is made. Here we introduce methods for
increasing error tolerance in this setting by using classical decision-making
to adaptively choose the bias in measurements as a fault tolerance protocol
proceeds. We study this technique in the setting of linear optical fusion based
quantum computing (FBQC). We provide examples demonstrating that by dynamically
arranging erasures, the loss tolerance can be tripled when compared to a static
arrangement of biased errors while using the same quantum resources: we show
that for the best FBQC architecture of Bartolucci et al. (2023) the threshold
increases from to per photon with the same resource state by
using dynamic biasing. Our method does not require any specific code structure
beyond having a syndrome graph representation. We have chosen to illustrate
these techniques using an architecture which is otherwise identical to that in
Bartolucci et al. (2023), but deployed together with other techniques, such as
different fusion networks, higher loss thresholds are possible