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Transmitting entanglement between light and matter in the metropolitan network of Barcelona –

Transmitting entanglement between light and matter in the metropolitan network of Barcelona

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Transmitting entanglement between light and matter in the metropolitan network of Barcelona
Measurement of non-classical correlations between remote locations. Map of the metropolitan area of Barcelona, with the three locations highlighted: ICFO, where the memory and SPDC source are located; CTTI, where the two optical fiber segments are connected; i2CAT, where the idler photons are detected. Credit: ICFO

As the efforts towards the realization of powerful quantum computers and quantum simulators continue, there is a parallel program aimed at attaining the quantum analog to the classical internet.

This new quantum network will provide ultrasecure, quantum-safe cybersecurity, and eventually will be devoted to the exchange of qubits, the unitary elements of quantum information, and the language of quantum computers. It will, in fact, provide a net over which different quantum computers could connect like classical processors are connected in cloud computing.

An up-front choice for the future quantum internet infrastructure is, in fact, the existing telecommunication network, which provides an almost ubiquitous channel over which light can travel very large distances with limited absorption. Because of this low absorption and its high speed, light is a great candidate as an information carrier, be it classical or quantum.

Bright laser light can be readily used to transfer classical information on the internet, while the attenuation of light in optical fibers is compensated by light amplifiers placed every ten km within these fibers. However, the transfer of quantum information—quantum communication—requires much more sophisticated means.

Quantum bits are still encoded in light, specifically , but this quantum encoding cannot be amplified because the rules of quantum mechanics prevent it; if you try to amplify the quantum encoding, you seriously damage the information contained in the photons. Thus, the amplifiers used in classical networks cannot be used for quantum bits. This means that a radically new technology is needed to build a quantum version of the internet: the quantum repeater.

As light amplifiers ensure connectivity between distant locations, quantum repeaters will allow for long distance communication by distributing entanglement between them.

Entanglement is an exclusively quantum property of two objects that show correlations that cannot be reproduced through classical means, and it is one of the primary components of quantum communication. It can be used to transfer quantum information, for example, through quantum teleportation between two nodes of a quantum repeater system.

One way of establishing remote entanglement between two nodes is through direct transmission: an entangled pair of photons can be generated, with one staying put while the other travels to the other location. This means that the latter must be compatible with optical fiber transmission, while the former must be stored in a , leading to entanglement between light and matter.

Now, one needs a set of quantum repeaters to pair several of these nodes to achieve long-distance entanglement between quantum memories. A promising architecture for these quantum repeater nodes relies on pairing the spontaneous generation of photon pairs, a process known as spontaneous down-conversion (SPDC), with an external quantum memory.

This is the approach that researchers at ICFO have taken. In a new study appearing on the arXiv preprint server, Jelena Rakonjac, Samuele Grandi, Soren Wengerowsky, Dario Lago-Rivera, and Felicien Appas, led by ICREA Prof. at ICFO Hugues de Riedmatten demonstrate the transmission of light-matter entanglement over tens of kilometers of optical fiber.

In their experiment, they generated pairs of photons, where one is emitted at the telecommunication wavelength of 1436nm, while the other is emitted at 606nm, compatible with the solid-state quantum memories used, realized in special crystals doped with rare-earth atoms.

They then tapped into the metropolitan network of Barcelona, connecting their system to two fibers that ran from ICFO, in Castelldefels, to the Telecommunication Centre of Catalunya (CTTI), en Hospitalet de Llobregat. By connecting both centers, they created a ring of 50 km, sending the photons all the way to downtown Barcelona and back to ICFO.

With this, they demonstrated that after a full round-trip of 50 km, the light generated in the lab maintains its quantum features without substantial decrease, showing that the photonic qubits do not manifest decoherence when traveling tens of km in a fiber optic cable, even in a metropolitan area. In short, quantum light left the lab, and it was ultimately detected back at its origin.

However, quantum communication requires using and verifying entanglement between remote locations, where entangled photons are detected in locations well-separated in space and time. Moving in this direction, the researchers extended their network to include a new node, this time located at the i2CAT foundation, a building in Barcelona, about 44 km from ICFO through the local optical fiber network and 17 km in a straight line.

There, they installed a telecom detector to measure the arrival of photons that came through one of the fibers while the other fiber was connected to a transducer, which turned the electrical signal of the detector into light and sent it through the optical fiber line.

This way, the information could be conveyed back to ICFO with high precision, even though the photon was detected about 17 km away. Moreover, they used the same transducers to send synchronization signals between the two nodes of this basic network, where the generation and detection of quantum correlations were fully separated between two independent yet connected nodes.

The experiment validated the system used by the researchers to generate light-matter entanglement and has proven to be one of the pioneering candidates for the realization of a quantum repeater node, the enabling technology for long-distance quantum communication. Proof-of-principle demonstrations have already been realized in the lab, and the group is now working on improving the performance of both the memory and the source.

Moreover, the researchers have partnered with Cellnex (Xarxa Roberta de Catalunya), and a new laboratory is available at the Collserola tower within the context of the QNetworks and EuroQCI Spain projects for the realization of an entangled state of remote quantum memories.

The realization of a long-distance backbone for entanglement distribution between quantum memories is also one of the main goals of the Quantum Internet Alliance (QIA), the leading European effort in the realization of the quantum internet of which ICFO is a main partner.

The results of this study, “namely the transmission of light-matter entanglement over fibers deployed in a metropolitan area, are the initial stepping stone towards the realization of a full-fledge quantum internet, with our source and memory quantum node at its core,” comments Samuele Grandi, a researcher at ICFO and co-first author of the study.

As ICREA Prof. at ICFO Hugues de Riedmatten concludes, “Light-matter entanglement is a key resource for and was demonstrated many times in the laboratory. Demonstrating it in the installed fiber network is a first step towards realizing a test-bed for technologies in the Barcelona area, preparing the ground for long-distance fiber-based networks.”

More information:
Jelena V. Rakonjac et al, Transmission of light-matter entanglement over a metropolitan network, arXiv (2023). DOI: 10.48550/arxiv.2304.05416

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Telecom-wavelength quantum repeater node transmits quantum information over tens of kilometers


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Public Health Specialist: Prevention, Care & Treatment (Harare) at U.S. Embassy In Zimbabwe – Pindula Jobs –


Comprehensive knowledge of current HIV/AIDS Prevention Care &Treatment (PC&T) issues including prevention strategies, behavior change, HIV testing, and treatment is required. In-depth knowledge of the range of PC&T programs, policies, regulations and precedents applicable to development and administration of national public health program is required. Detailed knowledge of the host government health care system and structures including familiarity with MOHCC policies, program priorities and regulations is required. In-depth knowledge of HIV/AIDS public health programs, strategies, methods, processes and techniques used to plan, develop, implement and evaluate results of prevention, care and treatment programs is required. Good working knowledge of overall administrative requirements, budgeting and fiscal management in support of contracts/cooperative agreements/grants/purchase requisitions is required.

Education Requirements:

Doctoral level degree (Doctor of Public Health (D.Ph.), Doctor of Medicine (MD) or Doctor of Philosophy (PhD) or host country equivalent degree in medicine, nursing, public health, epidemiology, behavioral science field is required.


LANGUAGE: English: Level 4 – Fluent; speaking/reading/writing, may include the ability to translate


Strong oral and written communications skills are required to develop and maintain effective, sustainable working relationships with national and international working partners and generate dissemination. Ability to analyze, understand and discuss program design, management and implementation approaches is required. This includes the development of evaluation designs, use of reliable and valid instruments and methods for data collection, and conducting data analysis. Ability to work across a wide range of complex situations and settings and to develop cooperative, collaborative and effective program strategies with diverse partners and stakeholder organizations. The specialist is expected to be innovative and have strong problem-solving skills to overcome challenges such as stakeholders’ resistance to accept new guidelines or program shifts, program implementation problems, resolving differences in approach between host government policies/priorities and PEPFAR priorities, and redirecting partner practices to conform to standards for HIV/AIDS prevention, treatment, and care. Intermediate user level of word processing, spreadsheets, and databases is required. Strong skills in data analysis, including interpretation of program monitoring and evaluation data and translating research findings into practice, are required. The ability to lead results-driven project teams and workgroups is required.

EQUAL EMPLOYMENT OPPORTUNITY (EEO): The U.S. Mission provides equal opportunity and fair and equitable treatment in employment to all people without regard to race, color, religion, sex, national origin, age, disability, political affiliation, marital status, or sexual orientation.

All applicants under consideration will be required to pass medical and security certifications.


How to Apply

Click here to apply

Deadline: 25 April 2024

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Driver (Kariba) at Family AIDS Caring Trust (FACT) – Pindula Jobs –

Job Description

Family AIDS Caring Trust Zimbabwe (FACT) is a Christian based organisation that was instituted in 1987. Since establishment, FACT Zimbabwe has been a leading national HIV and development organisation implementing various projects directly and through partnerships. The organization’s programming focuses on 4 strategic pillars Safeguarding and Sustainable Livelihoods (SSL), Health and Well-being (HW), Strategic Information and Research (SIR) and Organisational Efficiency and Effectiveness (OEE). FACT seeks the services of a Driver detailed below.

Reports to: Procurement and Logistics Assistant.

Duties and Responsibilities

  • Maintains vehicle log books and photocopies the current log sheet and fuel ledger and submits to the Senior Driver.
  • Checks to see if vehicles are due for service and takes vehicles for servicing and repairs.
  • Keeps vehicles clean all the time.
  • Initiates fuel procurement requests.
  • Supports teams on outreach activities.
  • Drives project staff to their project implementation areas.
  • Collects all commodities (fuel, stationery, furniture etc) procured for the office.
  • Reports incidents and breakdowns on the vehicles.
  • Checks to ensure all vehicles have fuel, oil, water, and other fluids.
  • Checks to ensure that all vehicles are licensed and insured by liaising with the Senior Driver.

Qualifications and Experience

  • Should have 5 O levels.
  • Driver’s licence should be at least 5 years.
  • At least 2 years accident-free driving as a professional driver.
  • Class 4 drivers’ licence, defensive driving certificate,


How to Apply

Click here and complete the form.

Send a detailed CV to:, highlighting the post.

Please ensure that both steps are carried out to complete the application process.

  • Background checks will be done for successful candidate to ensure child safeguarding and protection in all our work. FACT commits itself to protecting children whom its staff, volunteers as well as outsiders may get into contact with. The organization is mandated to serve the best interest of all children through protection from abuse, harm and exclusion, child participation and development in all its programs.
  • FACT is an equal opportunity employer which does not discriminate in terms of race, tribe, place of origin, political opinion, colour, creed, gender, pregnancy, HIV/AIDS status or, subject to the Disabled Persons Act [Chapter 17:01].

FACT does not charge a fee at any stage of the recruitment process.

NB: Only short listed candidates will be notified.

Deadline: 19 April 2024

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Heaviest black hole pair ever discovered – Sky at Night Magazine

A pair of supermassive black holes that have been trapped dancing around each other for billions of years have now been found to be the heaviest binary ever measured.

Though theory predicts that such pairs of supermassive black holes should merge together, the act of merging has never actually been seen.

The huge mass of this pair could help astronomers understand why such mergers are seemingly so rare.

The pair are located in B2 0402 379, an enormous ‘fossil cluster’ galaxy created when an entire cluster’s worth of galaxies and stars merged into a single giant elliptical.

The Final Parsec Problem concerns the merging of supermassive black holes in colliding galaxies. Credit: Draco-Zlat / Getty Images
Artist’s impression of merging black holes in colliding galaxies. Credit: Draco-Zlat / Getty Images

Most galaxies host a central supermassive black hole.

When galaxies merge, these begin orbiting around one another.

As they circle, they transfer some of their energy to the surrounding stars and gas – much of which is ejected in the process.

The more energy these black holes lose to the material around them, the closer they move towards each other. 

In the case of this binary pair, the black holes moved in until they were a mere 24 lightyears apart – the smallest such separation ever directly measured.

However, they have remained stuck at this distance for the last three billion years.

To understand why this might be the case, astronomers have used the Gemini North telescope’s Gemini Multi-Object Spectrograph (GMOS) to study the system.

The Gemini North telescope. Credit: International Gemini Observatory/NOIRLab/NSF/AURA/T. Slovinský
The Gemini North telescope. Credit: International Gemini Observatory/NOIRLab/NSF/AURA/T. Slovinský

“The excellent sensitivity of GMOS allowed us to map the stars’ increasing velocities as one looks closer to the galaxy’s centre,” says Roger Romani from Stanford University, who took part in the study.

“With that, we were able to infer the total mass of the black holes residing there.”

The binary is estimated to weigh in at 28 billion times that of the Sun, making it the heaviest ever measured.

As well as giving vital context to the formation of this specific binary system and its past within the galaxy, the measurement also gives support to the idea that the stalling of binary supermassive black holes is linked to their huge masses.

The amount of gas and stars that would have to be ejected in order to move such massive black holes this close to each other would be enormous. 

“Normally it seems that galaxies with lighter black hole pairs have enough stars and mass to drive the two together quickly,” says Romani.

“Since this pair is so heavy, it required lots of stars and gas to get the job done. But the binary has scoured the central galaxy of such matter, leaving it stalled.”

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