Conference PaperPDF Available

Adding store and forward features to quantum key distribution space network for secure global and space communications with cubesats

  • Ecuadorian Space Agency


At this moment, several space programs are under way to achieve the Technological Readiness Level (TRL) for the entanglement-based Quantum Key Distribution technique (QKD) in space, this technology is the corner stone in security for the next step towards a " Global Quantum Internet " in the near future. Space is the right scenario to deploy this technology because of the absorption problem with the Optical Networks on the Ground. We will review some of the more important initiatives in this field which includes the Chinese QUESS (Quantum Experiments at Space Scale) mission, and the QEYSSAT Canadian Mission of COM DEV Ltd. Both of them based on conventional-sized satellites, and also the SPEQS program of the Centre for Quantum Technology in National University of Singapore, proposed with a cubesat constellation. In this paper we will present a space program proposed between Quantum Aerospace Research Institute and the Ecuadorian Civilian Space Agency to develop and deploy an entanglement-based Quantum Key Distribution space based network to provide secure QKD communication at a Global Scale with Cubesat constellations, this technological infrastructure will also be the Core level for a QKD system for an Earth-Moon secure communications network. Actually the QKD technology is restricted only to line of sight scenarios, the challenge of the program will be to develop miniaturized Quantum Memories to add store and forward capabilities to the cubesats network to transport the entangled photons to different space coordinates even without line of sight.
Adding store and forward features to quantum key distribution
space network for secure global and space communications with
Mst. Jaime Jaramillo (1), Cdr. Ronnie Nader (CM3) (2)
(1) Quantum Aerospace Rsearch Institute (QAS)
Km 6.5 via Puembo, Quito, Ecuador,
Phone: +593-978-987367, Mail:
(2) Ecuadorian Civilian Space Agency (EXA)
Km 3.5 via a Samborondon, Guayaquil, Ecuador,
Phone: +593-999-658389, Mail:
1st IAA Latin American Symposium on Small Satellites:
Advanced Technologies and Distributed Systems
March 7 - 10, 2017
San Martín, Buenos Aires, Argentina
At this moment, several space programs are under way to achieve the Technological Readiness
Level (TRL) for the entanglement-based Quantum Key Distribution technique (QKD) in space, this
technology is the corner stone in security for the next step towards a “Global Quantum Internet” in
the near future. Space is the right scenario to deploy this technology because of the absorption
problem with the Optical Networks on the Ground.
We will review some of the more important initiatives in this field which includes the Chinese
QUESS (Quantum Experiments at Space Scale) mission, and the QEYSSAT Canadian Mission of
COM DEV Ltd. Both of them based on conventional-sized satellites, and also the SPEQS program
of the Centre for Quantum Technology in National University of Singapore, proposed with a
cubesat constellation.
In this paper we will present a space program proposed between Quantum Aerospace Research
Institute and the Ecuadorian Civilian Space Agency to develop and deploy an entanglement-based
Quantum Key Distribution space based network to provide secure QKD communication at a Global
Scale with Cubesat constellations, this technological infrastructure will also be the Core level for a
QKD system for an Earth-Moon secure communications network.
Actually the QKD technology is restricted only to line of sight scenarios, the challenge of the
program will be to develop miniaturized Quantum Memories to add store and forward capabilities
to the cubesats network to transport the entangled photons to different space coordinates even
without line of sight.
1 Introduction
For many years, the perspective of trying to create a global “Quantum Internet" [1], has been
pursued for a new generations of scientific teams around the world [2]. This Global “Quantum
Internet” will be based in a mature technology the for security: the Quantum Key Distribution
(QKD) technique, than establishes highly secure keys between two distant points using single
photons to transmit each qubit of the quantum key
Currently two approaches are been used to achieve this goal in parallel: fiber-based quantum
repeaters and direct satellite links. The fiber approach needs “Quantum Repeaters”(QR) to extend
the distance of elementary links by entanglement swapping [3, 4], While experimental
demonstration of short-range quantum communications has been effective demonstrated [5, 6], long
range repeater networks require the incorporation of fault-tolerant errorcorrection methods,and near
zero temperature to function adequately, numerous designs of quantum repeaters have been
proposed [7-13].
Terrestrial QKD networks using fibers optic cables or free-space atmospheric transmission are in
operation today, however, truly global distances are still very difficult to achieve for repeatersbased
on fiber links and quantum repeaters. This is true also for related approaches based on quantum
error correction [14], whichtend to require repeater stations that are only a few kilometers apart.
Satellites in Earth orbit represent the only feasible way using currently technology to provide global
distance QKD services, the advantage of quantum communication via satellites is that transmission
loss is dominated by diffraction rather than absorption and thus scales much more favorably with
distance. There has been a lot of progress in terms of feasibility studies and ongoing missions [15-
23],even with new generation fiber-based networks and quantum repeaters than can establish long
range quantum entanglement, most optimistic quantum repeater protocols may still only facilitate
distance up to about1000 km [24] on terrestrial links while very recent results show that a quantum
receiver based on satellite links are able to reach 10,000 km [25]
Finally a disrupted technology has appear in the horizon and is nothing less than sneaker-net
network approach. This approach to quantum information, introducing a new network mechanism
for the establishment of quantum entanglement over long distances based on the transport of error-
corrected quantum memories [26].
Quantum memories may be transported to locations where entanglement is required or to
intermediate locations to facilitate entanglement swapping between traditional quantum repeater
networks, enabling a complete network structure without the full deployment of physicallinks. It is
specially use fuel for transoceanic communication that presents a particular challenge for quantum
networking, with this proposal the entanglement will be establishment by ship.
In section two of this paper we will take a closer look to this approaches and their implications in
our proposal.
2 QKD Space Scenarios and ongoing Missions
A global, space-based network for distributing entangled photons will enable strongencryption keys
to be delivered securely between any two points on Earth. Entanglement-based QKD is a mature
technology. It has been demonstrated on multiple occasions and is the most established
technological application of entanglement.
At the time of writing this paper, two mission have been launch with QKD mission objectives, one
is the Chinese QUantum Experiments at Space Scale (QUESS) mission [27], and the other was the
Small Photon Entangling Quantum Systems (SPEQS) mission integrated in the Galassia
We think that the second of the two missions mentioned give us a clue of the path to be followed for
a Latin-American Science Space Program using a revolution in the space industry where the use of
very small spacecraft known as Nano-satellites are enabling access to space for a large number of
organizations with only modest funding, challenging more traditional platforms for space
Fig. 1.Scenarios for QKD in space.
The scenarios used until now for QKD space missions are showed in Fig. 1 (Courtesy of EPJ
Quantum Technology) [29].The possible satellite-based QKD implementations are: 1. Ground-to-
space,where the photon source is on the ground and the satellite only carries detectors. 2. Space-to-
ground, wherethe satellite carries a source and detectors. 3. A platform that can beam down to two
ground stationssimultaneously. 4. Inter-satellite QKD which could be the building block for a long
baseline test of quantumcorrelations. To enable configurations 2-4 with Bell violation-type
measurements, a source of entangledphotons in space must be demonstrated.
Both the QUESSmission [27]and the SPEQS mission [29] uses the scenario number three for the
QKD distribution, i.e. a space-based photon source platform that can beam photons down to two
ground stations simultaneously on earth to create a QKD channel between the two points, and then
perform a bell state measurement between then.Following this approach QUESS mission has
achieved the creation of an "intercontinental" QKD channel of 1200 Km between Beijing and
Vienna. [30]
A further theoretical work in this direction performed by a Canadian and Australian team [31],
shows that with the adding of quantum repeaters (QR) to this architecture, truly global distances can
be achieved. In this approach the satellites just need to be equipped with entangled pair sources,
while the more complex components, such as quantummemories (QM) and quantum non-
demolition (QND) detectors, are on the ground.
Fig. 2.Canadian-Australian Global QKD Satellite Network Architecture proposal.
Figure 2 shows the proposed architecture of the Canadian and Australian teams with quantum
repeaters on the ground and satellite quantum links. “. Each elementary link (of length Lo) consists
of an entangled photon pair source on a low-earthorbit satellite (at height h), and two ground
stations consisting of quantum non-demolition (QND) measurement devices and quantum memories
(QM). The successful transmissionof entangled photons to each ground station is heralded by the
QND devices, which detect the presence of a photon nondestructively and without revealing its
quantum state. The entanglement is then stored in the memories until information about successful
entanglement creation in two neighboring links is received. Then the entanglement can be extended
by entanglement swapping based on a Bell state measurement(BSM) [31]
An important variable to have in account in this architecture is that the satellite-based links are
active only during each time period when the satellite is visible from both ground stations (the flyby
time" TFB).For currently realistic quantum memory lifetimes all satellite links in Figure 2 have to
be active simultaneously, which implies that the architecture requires a number of satellites equal to
the number of links. However, the results show that four to eight links are sufficient to span global
The last mission concept we will analyze in this document is the NanoQEY (Nano Quantum
Encryption) a nanosatellite mission concept developed by the Institute of Quantum Computing at
the University of Waterloo and the Space Flight Laboratory at Institute of Aerospace Studies in the
University of Toronto that would demonstrate long distance QKD between two distant ground
stations on earth.
The primary object of the NanoQEY is to successfully distribute at least 10Kbits of secure key
between two optical ground stations separated by at least 400 Km during the life time of the
mission, the secondary objective of the NanoQEY mission is to perform a bell test for entangled
photons separated by at least 400 Km, where one photon shall be measured on ground and the other
on the satellite.
In order to securely distribute encryption keys, the NanoQEY satellite act as a “trusted node” in
wich the keys would be held during operations. The satellite would create a secure key between
itself and Ground Station A during one or more passes, and then create another secure key between
itself and ground station B during one or more passes. To create a secure key between Station A and
Station B, a Boolean combination of the two keys is calculated on the satellite. The result is
transmitted (classically) to one of the two ground stations. Using the combined key and the
knowledge of its own key, a station can then calculate the other station key and use it for secure
communications between themselves. [32]
After this review we can conclude that, Satellites in Earth orbit represent the only way using
currently feasible technology to provide global-distance QKD services. In the simplest
configurations, satellites could be used as complementary trusted nodes to bridge the distance
between geographically dispersed QKD ground networks. In the future quantum repeaters may be
developed which could establish long range quantum entanglement, however there will still be a
role for satellites as the currently most optimistic quantum repeater protocols may still only
facilitate distance up to about 1000 km [24] on terrestrial links while very recent results show that a
quantum receiver based on satellite links and quantum memories on ground are able to reach 10,000
km and beyond. [25]. It is clear that to operate on continental and global scales, it is anticipated that
future quantum networks would be similar to conventional data networks and employ both fiber-
based solutions (quantum-repeater-equipped) and links with optical quantum communication
3 The QAS-EXA “QSNet Space Program
Review of the state of the art low Earth orbit satellite quantum communication gives us the big
picture necessary to develop the proposal of our QSNet Space Program. This proposal will be
aligned with the major policy of our institutions:
Democratization of space technologies.
Develop of high efficient technology at a very low price to make it reachable for
developing countries.
We will clearly choose the nanosatellite technology to implement our mission, reduce budged and
fulfill our philosophy, in this line we find two major feasibility obstacles even with the best mission
proposal (Quantum Repeaters + Satellite Links [25]): first the only mission that have successfully
deploy a practical source of entangled photons in space until now is the Chinese QUESS, and it is
clearly not a nanosatellite mission, the second mission that proposes an entangled photon source on
space, the SPEQS mission, is a nanosatellite mission, not withstanding is still in the process of
achieve the necessary technological readiness level (TRL). Second: even with a cheap and
affordable nanosatellite quantum source, we still have a budged obstacle due to the operational
costs, because in the most optimistic scenario we will need at least 8 ground stations and operations
center on the Earth to operate a global QKD Network. This make this project only feasible for
major telecom and satellite operator worldwide, leaving behind the emerging actors and developing
countries forthis field.
Even more, the use of telescopes as ground stations of approximate 1,5-2m diameter [32]and a
system of optical fine pointing in the satellite, lead us to nanosatellites with dimensions like
40x26x20 cm3, at least [31], and this is not the scope of our work.
We propose a major technological shift to approach the problem; this is the change of the frequency
for the Quantum Chanel from optical domain to Radio Frequency Domain, specifically Microwaves
in the X Band. This major technological approach permit us to solve not only the miniaturization of
our spacecraft but also the miniaturization of the ground station, with the lower price that all that
Additional to all of this, our system will add store and forward facilities to the satellites using
Quantum Non Demolition Detectors (QND) and Radio Frequency Quantum Memories
(RFQM)[33], and a sneakernet approach [25] for quantum networks.This will create Mobile Nodes
in the space to transport entangled RF Photons from one place on Earth to a totally different
location even in non-line of sight scenarios as we will see.
3.1.- Proof of Concept Mission
The QSAT (Quantum Satellite) is a Proof of Concept nanosatellite mission developed by
Quantum Aerospace Research Institute (QAS) and the Ecuadorian Civilian Space Agency
(EXA), which would demonstrate quantum entanglement between intercontinental
distances by using a Mobile Quantum Repeater in Space. The quantum channel will be
established with micro wave technology. The QSAT mission will also count with a QKD
protocol that includes timing analysis, basis reconciliation, error corrections and privacy
amplification, this QKD protocol will use classical channels for transmission, and would
enable QKD transmission between the two ground stations on the ground.
3.1.1.-Mission Objectives
The scientific mission objectives of the proposed mission are the followings:
- Transmit an entangled RF photon from Ground Station 1 to QSAT Satellite.
- Transmit an entangled RF photon from QSAT Satellite to Ground Station 2.
- Perform a Bell State Measurement between RF photons in Ground station 1 and Ground
Station 2.
- Distribute QKD Keys between Ground Station 1 and Ground Station 2.
- Perform scientific experiments of quantum teleportation between Ground Station 1 and
Ground Station 2.
3.1.2.- Mission Architecture
Fig. Conceptual Design QSAT Proof of Concept Mission
The conceptual design of the space craft was achieved using the PEGASUS Class
technology of the Ecuadorian Civilian Space Agency (EXA), that include on board
computer and radios, GPS receiver system, IMU system, high capacity batteries, etc. with
this technology the QSAT would be developed in a standard 3 cube sat U package of
10x10x30 cm3. The compound deployable solar array (DSA/3A) with six 3U solar panels
will generate a peak power generation of 100.8 Watts, and the high capacity battery banks
have a total nominal capacity of 427.2 Watts, having ample power to perform in eclipse.
The spacecraft will have a four patch, X-Band antenna array in which would be allocated
the 3 links necessary for the correct operation of the mission including the quantum link, the
antenna array will be operated using artificial muscle technology from the EXA,
specifically the MDH/R2 model so that it can be pointed inward in order to concentrate the
transmission beam photon flux over a very small footprint and therefore boosting the gain
in many orders of magnitude for the ground station 1 and 2. Fig.3 shows the conceptual
design of the QSAT.
Fig. QSAT Dynamic Comunications array based on artificial muscle
technology boosting the gain of the array by concentrating the photon flux of the
phasing beams
The QSAT would be launched into a 400 Km – 600 Km orbit and a 98 degree inclination
mean LTAN (Local Time of ascending node) of noon +/- 11h00 to 12h00 The mission
would employ the HERMES-A ground station in Guayaquil working as Ground Station 1
and a Ground Station in Holland working as Ground Station 2.
3.1.3. Concept of operations
The minimum mission duration would be one year from launch. The life time of the EXA
PEGASUS Class technology in which the QSAT would be based in fact has proven at least
3 years of life time in space, but we think that one year will be enough time to achieve the
scientific objectives of the mission.
To fulfill the mission objectives the system will have three links between Ground Station
and Satellite, the TT&C link would operate in UHF band, the Data Link and Housekeeping,
including QKD protocol will operate in S Band, andfinally the Quantum Channel will be
implemented in X Band. Additionally the QSAT and the Ground Stations 1 and 2 would
need GPS receiver technology to achieve the pointing degree needed for scientific
Station 1
Station 1
QKD Protocol &
Data Housekeeping
Station 1
Up Link
Down Link
Station 2
Station 2
QKD protocol &
Data Housekeeping
Up Link
Bell State
Measurement Clasic Chanell
Down Link
Distancia Intercontinental
Fig. 4.QSNet proof of concept mission system overview
During nominal operations QSAT would be oriented for optimal power generation and
thermal control. As the satellite approaches a ground station it will point it using the beacon
if it is Ground Station number 1, the QKD protocol will set the RF Quantum Source on the
ground station to emit a pair of entangled RF microwaves, the QKD protocol also will set
the RF QND to start detection and the RFQM of the QSAT to store the RF Quantum photon
emitted from the ground station. When QSAT arrives to Ground Station number 2, the
QKD protocol will set the RFQM to emit the RF photon, and the will set the QND and the
RFQM of ground station 2 to receive the RF photon. Fig. 4. Shows this operation concept.
Up Link
Banda X
Down Link
Banda X
Orbita QSat-01
Orbita QSat-01
Orbita Qsat-01
Fig.5. Intercontinental distance entanglement
This concept of operations will permit QSAT for the first time to transmit an entangled RF
Quantum photon from Ground Station 1 (Ecuador - Latin America) to Ground Station 2
(Delft Holland) over an intercontinental distance (approximate 10000 Km). Fig. 5. Shows
this feature.
Fig. 6.Intercontinantal Distance BSM
The major concern in this topology will be perform the Bell State Measurement (BSM)
between the RF photons in the two ground stations over a continental distance, this is
something that still haven’t been tested by any scientific team. Fig. 6 shows this schema
Quantum Payload Design
For the proposed QSAT Mission, QAS has designed a new technology quantum payload
based on the RF quantum Technology [34] that would be compatible with the mass volume,
power and performance constrains of a low-cost nanosatellite platform.
The technological basis of payload is adding RFQM and QND [33] to the nanosatellite,
turning it in to a mobile quantum repeater, than can be used in a sneakernet approach [25].
The key research during the maturation of technology process will be focus on the
development of a forward error correction technique to achieve a RF quantum memory
storage period needed for the mission, also we would need a QND and RFQM on demand
process based on the state of the art Micro wave Quantum Technology [34]
House Keeping Start Tracker GPS Power
Electronics Analysis
and Control
RF Quantum
Banda X
Link Up
Fig. 7. Quantum Payload Block Diagram
Fig. 7 provides a simplified Block Diagram of the Quantum payload of QSAT, in this
diagram the Forward error correction circuit is inside the electronics analysis and control
A further Global QKD distribution space network will be designed in base of the result of
the Proof of Concept mission, this will also include the possibility to distribute QKD on to
the space.
4. Programmatic
The proposed Space Program will be supported for all the Nano Satellite Space Technology
developed by the Ecuadorian Space Agency (EXA) and the INSPIRE consortium, it would permit a
rapid deployment of the Space Program. Notwithstanding the Payload and the Optical Ground
Station will need additional maturation technology process.
The milestones for the Technology Readiness Level (TRL) of the proposed Space Program is
shown in Table 1
2017 Payload Technology Maturation QAS Laboratories
2017 Ground Station Technology Maturation QAS Laboratories
2018 Drone Test / High Altitude Test
Aerospace / High
2019-2022 Proof of Concept Mission Low Earth Orbit
2023-2027 QSNet Technological Deploy Low Earth Orbit
Table 1.QSNet Space Program Milestone
The low cost, high efficient and mature Nano satellite space technology of EXA would allow to
develop the proposed QSAT Proof of Concept Mission in 2.75 years from project kick-off to launch
of space craft, followed by 1 year on-orbit mission. Table2 shows a summarized project schedule
for QSNet proof of concept mission.
Mission Funding
Preliminary Design
Detailed Design and Miniaturization
Manufacture, Assembly, Test
On Orbit Operations
Table 2. Quantum Space Network QSAT proof of concept mission schedule
5. Conclusions
The feasibility study performed by QAS and EXA show that a nanosatellite mission to demonstrate
quantum entanglement over intercontinental distances is feasible and practical with a maturation
process of current technology. QSAT will employ proven space technology from EXA to
implement the space craft and a innovative compact QKD Payload designed by QAS that would be
compatible with the mass, volume, power and performance constrains of low cost nanosatellite
If it is constructed under the high efficiency approach of EXA, after one year of technology
maturation, the proposed QSAT mission would be developed in 2.75 years, from kick-off to launch
of the spacecraft, followed by one year on orbit mission.
If the mission achieve all the scientific mission objectives, first it would be a new world record for
quantum entanglement, second it would demonstrate de feasibility of a Global QKD Space Network
based on this technology, adding to this that with the RF used in the project we will open the
possibility that any parson could afford a low-price ground station to securely communicate point to
point with any other place in the world, with all that this means.
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A working free-space quantum key distribution system has been developed and tested over an outdoor optical path of ~1 km at Los Alamos National Laboratory under nighttime conditions. Results show that free-space quantum key distribution can provide secure real-time key distribution between parties who have a need to communicate secretly. Finally, we examine the feasibility of surface to satellite quantum key distribution.
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Quantum entanglement is the central resource behind applications in quantum information science, from quantum computers and simulators of complex quantum systems to metrology and secure communication. All of these applications require the quantum control of large networks of quantum bits (qubits) to realize gains and speedups over conventional devices. However, propagating quantum entanglement generally becomes difficult or impossible as the system grows in size, owing to the inevitable decoherence from the complexity of connections between the qubits and increased couplings to the environment. Here, we demonstrate the first step in a modular approach to scaling entanglement by utilizing a hierarchy of quantum buses on a collection of three atomic ion qubits stored in two remote ion trap modules. Entanglement within a module is achieved with deterministic near-field interactions through phonons, and remote entanglement between modules is achieved through a probabilistic interaction through photons. This minimal system allows us to address generic issues in synchronization and scalability of entanglement with multiple buses, while pointing the way toward a modular large-scale quantum computer architecture that promises less spectral crowding and less decoherence. We generate this modular entanglement faster than the observed qubit decoherence rate, thus the system can be scaled to much larger dimensions by adding more modules.
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Quantum communication holds promise for unconditionally secure transmission of secret messages and faithful transfer of unknown quantum states. Photons appear to be the medium of choice for quantum communication. Owing to photon losses, robust quantum communication over long lossy channels requires quantum repeaters. It is widely believed that a necessary and highly demanding requirement for quantum repeaters is the existence of matter quantum memories at the repeater nodes. Here we show that such a requirement is, in fact, unnecessary by introducing the concept of all photonic quantum repeaters based on flying qubits. As an example of the realization of this concept, we present a protocol based on photonic cluster state machine guns and a loss-tolerant measurement equipped with local high-speed active feedforwards. We show that, with such an all photonic quantum repeater, the communication efficiency still scales polynomially with the channel distance. Our result paves a new route toward quantum repeaters with efficient single-photon sources rather than matter quantum memories.
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Optical quantum communication utilizing satellite platforms has the potential to extend the reach of quantum key distribution (QKD) from terrestrial limits of ~200 km to global scales. We have developed a thorough numerical simulation using realistic simulated orbits and incorporating the effects of pointing error, diffraction, atmosphere and telescope design, to obtain estimates of the loss and background noise which a satellite-based system would experience. Combining with quantum optics simulations of sources and detection, we determine the length of secure key for QKD, as well as entanglement visibility and achievable distances for fundamental experiments. We analyze the performance of a low Earth orbit (LEO) satellite for downlink and uplink scenarios of the quantum optical signals. We argue that the advantages of locating the quantum source on the ground justify a greater scientific interest in an uplink as compared to a downlink. An uplink with a ground transmitter of at least 25 cm diameter and a 30 cm receiver telescope on the satellite could be used to successfully perform QKD multiple times per week with either an entangled photon source or with a weak coherent pulse source, as well as perform long-distance Bell tests and quantum teleportation. Our model helps to resolve important design considerations such as operating wavelength, type and specifications of sources and detectors, telescope designs, specific orbits and ground station locations, in view of anticipated overall system performance.
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We examine the possibility of secure key exchange between a ground station and a low earth orbit satellite using the technique of quantum cryptography. The study suggests there are no technical obstacles to building a system that could exchange keys at kilobaud rates between a metre diameter telescope on the ground and a satellite with a 10 cm diameter lightweight telescope.
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Sending satellites equipped with quantum technologies into space will be the first step towards a global quantum-communication network. As Thomas Jennewein and Brendon Higgins explain, these systems will also enable physicists to test fundamental physics in new regimes.
Future multiphoton applications of quantum optics and quantum information science require quantum memories that simultaneously store many photon states, each encoded into a different optical mode, and enable one to select the mapping between any input and a specific retrieved mode during storage. Here we show, with the example of a quantum repeater, how to employ spectrally multiplexed states and memories with fixed storage times that allow such mapping between spectral modes. Furthermore, using a Ti:Tm:LiNbO_{3} waveguide cooled to 3 K, a phase modulator, and a spectral filter, we demonstrate storage followed by the required feed-forward-controlled frequency manipulation with time-bin qubits encoded into up to 26 multiplexed spectral modes and 97% fidelity.
Quantum repeaters (QRs) provide a way of enabling long distance quantum communication by establishing entangled qubits between remote locations. We investigate a new approach to QRs in which quantum information can be faithfully transmitted via a noisy channel without the use of long distance teleportation, thus eliminating the need to establish remote entangled links. Our approach makes use of small encoding blocks to fault-tolerantly correct both operational and photon loss errors. We describe a way to optimize the resource requirement for these QRs with the aim of the generation of a secure key. Numerical calculations indicate that the number of quantum memory bits required for our scheme has favorable poly-logarithmic scaling with the distance across which the communication is desired.