11 research outputs found
Quantum preparation uncertainty and lack of information
The quantum uncertainty principle famously predicts that there exist
measurements that are inherently incompatible, in the sense that their outcomes
cannot be predicted simultaneously. In contrast, no such uncertainty exists in
the classical domain, where all uncertainty results from ignorance about the
exact state of the physical system. Here, we critically examine the concept of
preparation uncertainty and ask whether similarly in the quantum regime, some
of the uncertainty that we observe can actually also be understood as a lack of
information (LOI), albeit a lack of quantum information. We answer this
question affirmatively by showing that for the well known measurements employed
in BB84 quantum key distribution, the amount of uncertainty can indeed be
related to the amount of available information about additional registers
determining the choice of the measurement. We proceed to show that also for
other measurements the amount of uncertainty is in part connected to a LOI.
Finally, we discuss the conceptual implications of our observation to the
security of cryptographic protocols that make use of BB84 states.Comment: 7+15 pages, 4 figures. v2: expanded "Discussion" section, "Methods"
section moved before "Results" section, published versio
Near-term quantum-repeater experiments with nitrogen-vacancy centers: Overcoming the limitations of direct transmission
Quantum channels enable the implementation of communication tasks
inaccessible to their classical counterparts. The most famous example is the
distribution of secret key. However, in the absence of quantum repeaters, the
rate at which these tasks can be performed is dictated by the losses in the
quantum channel. In practice, channel losses have limited the reach of quantum
protocols to short distances. Quantum repeaters have the potential to
significantly increase the rates and reach beyond the limits of direct
transmission. However, no experimental implementation has overcome the direct
transmission threshold. Here, we propose three quantum repeater schemes and
assess their ability to generate secret key when implemented on a setup using
nitrogen-vacancy (NV) centers in diamond with near-term experimental
parameters. We find that one of these schemes - the so-called single-photon
scheme, requiring no quantum storage - has the ability to surpass the capacity
- the highest secret-key rate achievable with direct transmission - by a factor
of 7 for a distance of approximately 9.2 km with near-term parameters,
establishing it as a prime candidate for the first experimental realization of
a quantum repeater.Comment: 19+17 pages, 17 figures. v2: added "Discussion and future outlook"
section and expanded introduction, published versio
All-photonic multiplexed quantum repeaters based on concatenated bosonic and discrete-variable quantum codes
Long distance quantum communication will require the use of quantum repeaters
to overcome the exponential attenuation of signal with distance. One class of
such repeaters utilizes quantum error correction to overcome losses in the
communication channel. Here we propose a novel strategy of using the bosonic
Gottesman-Kitaev-Preskill (GKP) code in a two-way repeater architecture with
multiplexing. The crucial feature of the GKP code that we make use of is the
fact that GKP qubits easily admit deterministic two-qubit gates, hence allowing
for multiplexing without the need for generating large cluster states as
required in previous all-photonic architectures based on discrete-variable
codes. Moreover, alleviating the need for such clique-clusters entails that we
are no longer limited to extraction of at most one end-to-end entangled pair
from a single protocol run. In fact, thanks to the availability of the analog
information generated during the measurements of the GKP qubits, we can design
better entanglement swapping procedures in which we connect links based on
their estimated quality. This enables us to use all the multiplexed links so
that large number of links from a single protocol run can contribute to the
generation of the end-to-end entanglement. We find that our architecture allows
for high-rate end-to-end entanglement generation and is resilient to
imperfections arising from finite squeezing in the GKP state preparation and
homodyne detection inefficiency. In particular we show that long-distance
quantum communication over more than 1000 km is possible even with less than 13
dB of GKP squeezing. We also quantify the number of GKP qubits needed for the
implementation of our scheme and find that for good hardware parameters our
scheme requires around GKP qubits per repeater per protocol run.Comment: 31 + 25 pages, 40 figure
Resource-efficient fault-tolerant one-way quantum repeater with code concatenation
One-way quantum repeaters where loss and operational errors are counteracted
by quantum error correcting codes can ensure fast and reliable qubit
transmission in quantum networks. It is crucial that the resource requirements
of such repeaters, for example, the number of qubits per repeater node and the
complexity of the quantum error correcting operations are kept to a minimum to
allow for near-future implementations. To this end, we propose a one-way
quantum repeater that targets both the loss and operational error rates in a
communication channel in a resource-efficient manner using code concatenation.
Specifically, we consider a tree-cluster code as an inner loss-tolerant code
concatenated with an outer 5-qubit code for protection against Pauli errors.
Adopting flag-based stabilizer measurements, we show that intercontinental
distances of up to 10,000 km can be bridged with a minimal resource overhead by
interspersing repeater nodes that each specializes in suppressing either loss
or operational errors. Our work demonstrates how tailored error-correcting
codes can significantly lower the experimental requirements for long-distance
quantum communication.Comment: 25 pages, 16 figures, 4 table
NetSquid, a NETwork Simulator for QUantum Information using Discrete events
In order to bring quantum networks into the real world, we would like to
determine the requirements of quantum network protocols including the
underlying quantum hardware. Because detailed architecture proposals are
generally too complex for mathematical analysis, it is natural to employ
numerical simulation. Here we introduce NetSquid, the NETwork Simulator for
QUantum Information using Discrete events, a discrete-event based platform for
simulating all aspects of quantum networks and modular quantum computing
systems, ranging from the physical layer and its control plane up to the
application level. We study several use cases to showcase NetSquid's power,
including detailed physical layer simulations of repeater chains based on
nitrogen vacancy centres in diamond as well as atomic ensembles. We also study
the control plane of a quantum switch beyond its analytically known regime, and
showcase NetSquid's ability to investigate large networks by simulating
entanglement distribution over a chain of up to one thousand nodes.Comment: NetSquid is freely available at https://netsquid.org; refined main
text section
Experimental study of quantum uncertainty from lack of information
Quantum uncertainty is a well-known property of quantum mechanics that states
the impossibility of predicting measurement outcomes of multiple incompatible
observables simultaneously. In contrast, the uncertainty in the classical
domain comes from the lack of information about the exact state of the system.
One may naturally ask, whether the quantum uncertainty is indeed a fully
intrinsic property of the quantum theory, or whether similarly to the classical
domain lack of knowledge about specific parts of the physical system might be
the source of this uncertainty. This question has been addressed in the
previous literature where the authors argue that in the entropic formulation of
the uncertainty principle that can be illustrated using the, so-called,
guessing games, indeed such lack of information has a significant contribution
to the arising quantum uncertainty. Here we investigate this issue
experimentally by implementing the corresponding two-dimensional and
three-dimensional guessing games. Our results confirm that within the
guessing-game framework, the quantum uncertainty to a large extent relies on
the fact that quantum information determining the key properties of the game is
stored in the degrees of freedom that remain inaccessible to the guessing
party. Moreover, we offer an experimentally compact method to construct the
high-dimensional Fourier gate which is a major building block for various tasks
in quantum computation, quantum communication, and quantum metrology.Comment: close to the version published in npj quantum informatio
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Resource-efficient fault-tolerant one-way quantum repeater with code concatenation
One-way quantum repeaters where loss and operational errors are counteracted by quantum error-correcting codes can ensure fast and reliable qubit transmission in quantum networks. It is crucial that the resource requirements of such repeaters, for example, the number of qubits per repeater node and the complexity of the quantum error-correcting operations are kept to a minimum to allow for near-future implementations. To this end, we propose a one-way quantum repeater that targets both the loss and operational error rates in a communication channel in a resource-efficient manner using code concatenation. Specifically, we consider a tree-cluster code as an inner loss-tolerant code concatenated with an outer 5-qubit code for protection against Pauli errors. Adopting flag-based stabilizer measurements, we show that intercontinental distances of up to 10,000 km can be bridged with a minimized resource overhead by interspersing repeater nodes that each specialize in suppressing either loss or operational errors. Our work demonstrates how tailored error-correcting codes can significantly lower the experimental requirements for long-distance quantum communication
Resource-efficient fault-tolerant one-way quantum repeater with code concatenation
One-way quantum repeaters where loss and operational errors are counteracted by quantum error-correcting codes can ensure fast and reliable qubit transmission in quantum networks. It is crucial that the resource requirements of such repeaters, for example, the number of qubits per repeater node and the complexity of the quantum error-correcting operations are kept to a minimum to allow for near-future implementations. To this end, we propose a one-way quantum repeater that targets both the loss and operational error rates in a communication channel in a resource-efficient manner using code concatenation. Specifically, we consider a tree-cluster code as an inner loss-tolerant code concatenated with an outer 5-qubit code for protection against Pauli errors. Adopting flag-based stabilizer measurements, we show that intercontinental distances of up to 10,000 km can be bridged with a minimized resource overhead by interspersing repeater nodes that each specialize in suppressing either loss or operational errors. Our work demonstrates how tailored error-correcting codes can significantly lower the experimental requirements for long-distance quantum communication.QID/Wehner GroupQN/Borregaard groe