#quantum memory

Physicists from the University of Basel have developed a memory that can store photons. These quantum particles travel at the speed of light and are thus suitable for high-speed data transfer. The researchers were able to store them in an atomic vapor and read them out again later without altering their quantum mechanical properties too much. This memory technology is simple and fast and it could find application in a future quantum Internet. The journal Physical Review Letters has published the results.

Even today, fast data transfer in telecommunication networks employs short light pulses. Ultra broadband technology uses optical fiber links through which information can be transferred at the speed of light. At the receiver's end, the transmitted information has to be stored quickly and without errors so that it can be processed further electronically on computers. To avoid transmission errors, each bit of information is encoded in relatively strong light pulses that each contain at least several hundreds of photons.

For several years, researchers all over the world have been working on operating such networks with single photons. Encoding one bit per photon is not only very efficient, but it also allows for a radically new form of information processing based on the laws of quantum physics. These laws allow a single photon to encode not only the states 0 or 1 of a classic bit, but also to encode a superposition of both states at the same time. Such quantum bits are the basis for quantum information processing that could make unconditionally secure communication and super fast quantum computers possible in the future. The ability to store and retrieve single photons from a quantum memory is a key element for these technologies, which is intensively investigated.

Simple and fast

A team of physicists led by the professors Philipp Treutlein and Richard Warburton from the University of Basel has now developed a particularly simple and fast quantum memory that stores photons in a gas of rubidium atoms. A laser controls the storage and retrieval processes. The technology used does not require cooling devices or complicated vacuum equipment and can be implemented in a highly compact setup. The researchers were also able to verify that the memory has a very low noise level and is suitable for single photons.

One step closer to the quantum internet

"The combination of a simple setup, high bandwidth and low noise level is very promising for future application in quantum networks," says Janik Wolters, first author of the study. The development of such quantum networks is one of the goals of the National Center of Competence in Quantum Science and Technology (NCCR QSIT) and of the EU Framework Programme for Research and Innovation that have funded this study. In the future, quantum networks could lead to unconditionally secure communication, the networking of different quantum computers and the simulation of complex physical, chemical and biological systems.

Simple Atomic Quantum Memory Suitable for Semiconductor Quantum Dot Single Photons Janik Wolters, Gianni Buser, Andrew Horsley, Lucas Béguin, Andreas Jöckel, Jan-Philipp Jahn, Richard J. Warburton, and Philipp Treutlein Phys. Rev. Lett. 119, 060502 – Published 8 August 2017

DOI: https://doi.org/10.1103/PhysRevLett.119.060502

Bright lasers

There is an article on nature.com about "Coherent storage and manipulation of broadband photons via dynamically controlled Autler-Townes splitting" and I am sure that to most of us that is just science fiction or "words that grow-ups use so we, the kids, do not understand their booty calls" :)

Photonic quantum information technologies rely on quantum memory for long-lived storage and coherent manipulation of short pulses of non-classical light. The optical quantum memories explored over the past two decades are based on various coherent light-matter interaction schemes, but despite impressive progress, practical memories featuring efficient, broadband and long-lived operation remain elusive, due to the technical demands and inherent limitations of the established schemes. Here, we introduce a technique for high-speed quantum memory and manipulation that overcomes these obstacles. This scheme relies on dynamically controlled absorption of light via the ‘Autler–Townes effect’, which mediates reversible transfer between photonic coherence and the collective ground-state coherence of the storage medium. We experimentally demonstrate proof-of-concept storage and signal processing capabilities of our protocol in a laser-cooled gas of rubidium atoms, including storage of nanoseconds-long single-photon-level laser pulses for up to a microsecond. This approach opens up new avenues in quantum optics, with immediate applications on atomic and solid-state platforms.

As I said. This is the "easy" part of the article and it has about 60 references :)

You will say, ok but what does it mean? Well, it means something on the line of "Really bright lasers that open up the atoms/atomic gas? which will then be used to store qubits"

So, using a bright laser. As someone else put it. Use a bigger hammer to fit stuff :)

In the quantum world and quantum computers, the quantum information (qubits) are transported using light (one photon = one qubit). The problem is STORING said qubit (photon) which, as you might know, are moving very very fast. So far they tried storing said photon in a very very cold gas which would do the trick but then you will need the photon (qubit) later you will have to take it out from there. So, we have slowly and carefully stored a qubit vs hammer it there with a laser.

One atom in the gas can have three states: - ground state, basically the natural state where the atom chills with his friends having a good beer (Carlsberg maybe?) - storage state basically is where the atom ends up after having the "drink" (absorbed the qubit) - transfer state, In this state the atom receives high energy necessary for qubit via a laser which stores the qubit and then changes the state from transfer to storage state. If the laser continues to shine on a stored atom it will change the state again from Storage to Transfer and the qubit is emitted as a photon again. Thus, the write/read is achieved.

By contrast, if you turn the laser off the qubit get stuck in storage state until you turn the laser back on. This works really well but it has some problems. Qubit has to have the same wavelength and the pulse of light has to be very long. Making the memory slow and, oh well, delicate.

The hammer way

Same states but this time very bright laser. If you change the power output of the laser the atom itself changes. It gives a good shake to the atom making contract and stretches making the transfer state split into two different states with a slightly different energy. This might mean that the photon will NOT be ideal for this BUT we only need the photon to overlap a bit with the wavelengths. If that is achieved then the Storage qubit state is reached. Researchers managed to prove exactly that. The researchers also have shown that their storage system is flexible because of the ability to change qubit properties. Imagine that in order to store an upcoming photon we just turn the power up on the laser and we zap it enough to absorb the photo. How about if we need the photon to come out with a specific energy? Make use of the laser control at low power to emit the qubit.

This method has the advantage of being faster than the current procedures. The control pulse is short and powerful and it stores qubits in the form of short pulses. It has the added value that we do not need to know the wavelength of the upcoming qubit. If it is the expected range we can interact with it. It can also use its adaptiveness in the case of two quantum systems. One requiring specific qubit wavelength while the other has a short duration. This read/write can convert.

Quantum computers and quantum systems are mindblowing if you think about them. Microwave systems for computation, photonic systems for transport and atomic states for memory. What an interesting and sometimes (I guess) frustrating field to be in.

The Quantum Middle Man

2 Jul 2015

Researchers at the Okinawa Institute of Science and Technology Graduate University (OIST) have identified a system that could store quantum information for longer times, which is critical for the future of quantum computing. This study was recently published in Physical Review Letters.

Quantum computing -- which aims to use particles on the atomic scale to make calculations and store the results -- has the potential to solve some key problems much faster than current computers.

To make quantum computing a reality, scientists must find a system that remains stable long enough to make the calculations. While this is an extremely short time frame, only thousandths of a second, the particles involved are so small that they are easily influenced by their surroundings. If the motion of the particles is disturbed, even a little, it throws off the whole calculation.

Nuclei are promising contenders for quantum memory because they are not easily influenced by their surroundings. However, that also makes them extremely difficult to manipulate. Many quantum physicists have tried with little success.

“In usual materials it is very difficult to control nuclei directly,” said Prof. Denis Konstantinov, who runs the Quantum Dynamics Unit at OIST.

Instead of trying control the nucleus directly, the researchers focused on a “middle man” of sorts – the electrons orbiting the nucleus.

Continue reading

Scientists ‘freeze’ light for an entire minute

In what could prove to be a major breakthrough in quantum memory storage and information processing, German researchers have frozen the fastest thing in the universe: light. And they did so for a record-breaking one minute.

It sounds weird and it is. The reason for wanting to hold light in its place (aside from the sheer awesomeness of it) is to ensure that it retains its quantum coherence properties (i.e. its information state), thus making it possible to build light-based quantum memory. And the longer that light can be held, the better as far as computation is concerned. Accordingly, it could allow for more secure quantum communications over longer distances.

Read the Rest: http://themindunleashed.org/2014/02/scientists-freeze-light-entire-minute.html

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Quantum memory 'world record' smashed

A fragile quantum memory state has been held stable at room temperature for a "world record" 39 minutes - overcoming a key barrier to ultrafast computers.