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Category: quantum physics

Quantum key distribution is one kind of important cryptographic protocols based on quantum mechanics, in which any outside eavesdropper attempting to obtain the secret key shared by two users will be detected. The successful detection comes from Heisenberg’s uncertainty principle: the measurement of a quantum system, which is required to obtain information of that system, will generally disturb it. The disturbances provide two users with the information that there exists an outside eavesdropper, and they can therefore abort the communication. Nowadays, most people need to share some of their private information for certain services such as products recommendation for online shopping and collaborations between two companies depending on their comm interests. Private Set Intersection Cardinality (PSI-CA) and Private Set Union Cardinality (PSU-CA), which are two primitives in cryptography, involve two or more users who intend to obtain the cardinalities of the intersection and the union of their private sets through the minimum information disclosure of their sets1,2,3.

The definition of Private Set Intersection (PSI), also called Private Matching (PM), was proposed by Freedman4. They employed balanced hashing and homomorphic encryption to design two PSI protocols and also investigated some variants of PSI. In 2012, Cristofaro et al.1 developed several PSI-CA and PSU-CA protocols with linear computation and communication complexity based on the Diffie-Hellman key exchange which blinds the private information. Their protocols were the most efficient compared with the previous classical related ones. There are also other classical PSI-CA or PSU-CA protocols5,6,7,8. Nevertheless, the security of these protocols relies on the unproven difficulty assumptions, such as discrete logarithm, factoring, and quadratic residues assumptions, which will be insecure when quantum computers are available9,10,11.

For the sake of improving the security of PSI-CA protocols for two parties, Shi et al.3 designed a probabilistic protocol where multi-qubit entangled states, complicated oracle operators, and measurements in high N-dimensional Hilbert space were utilized. And the same method in Ref.3 was later used to develop a PSI-CA protocol for multiple parties12. For easy implementation of a protocol, Shi et al.13 leveraged Bell states to construct another protocol for PSI-CA and PSU-CA problems that was more practical than that in Ref.3. In both protocols Ref.3 and Ref.13, only two parties who intend to get the cardinalities of the intersection and the union of their private sets are involved. Although Ref.12 works for multiple parties, it only solves the PSI-CA problem and requires multi-qubit entangled states, complicated oracle operators, and measurements. It then interests us that how we could design a more practical protocol for multiple parties to simultaneously solve PSI-CA and PSU-CA problems. Inspired by Shi et al.’s work, we are thus trying to design a three-party protocol to solve PSI-CA and PSU-CA problems, where every two and three parties can obtain the cardinalities of the intersection and the union of their respective private sets with the aid of a semi-honest third party (TP). TP is semi-honest means that he loyally executes the protocol, makes a note of all the intermediate results, and might desire to take other parties’ private information, but he cannot collude with dishonest parties. We then give a detailed analysis of the presented protocol’s security. Besides, the influence of six typical kinds of Markovian noise on our protocol is also analyzed.

Continue reading “Three-party quantum private computation of cardinalities of set intersection and union based on GHZ states” | >

Super-fast quantum computers and communication devices could revolutionize countless aspects of our lives—but first, researchers need a fast, efficient source of the entangled pairs of photons such systems use to transmit and manipulate information. Researchers at Stevens Institute of Technology have done just that, not only creating a chip-based photon source 100 times more efficient that previously possible, but bringing massive quantum device integration within reach.

“It’s long been suspected that this was possible in theory, but we’re the first to show it in practice,” said Yuping Huang, Gallagher associate professor of physics and director of the Center for Quantum Science and Engineering.

To create , researchers trap light in carefully sculpted nanoscale microcavities; as light circulates in the cavity, its photons resonate and split into entangled pairs. But there’s a catch: at present, such systems are extremely inefficient, requiring a torrent of incoming laser light comprising hundreds of millions of photons before a single entangled photon pair will grudgingly drip out at the other end.

Continue reading “Researchers create entangled photons 100 times more efficiently than previously possible” | >

University of Copenhagen researchers have advanced their quantum technology to such a degree that classical computing technology can no longer keep up. They have developed a chip that, with financial backing, could be scaled up and used to build the quantum simulator of the future. Their results are now published in Science Advances.

First came Google. Now, researchers at the University of Copenhagen’s Niels Bohr Institute in collaboration with University of Bochum have joined Google in the race to build the world’s first quantum computer with what they are calling a “major breakthrough.”

“We now possess the tool that makes it possible to build a quantum simulator that can outperform a classical computer. This is a major breakthrough and the first step into uncharted territory in the world of quantum physics,” asserts Professor Peter Lodahl, Director of the Center for Hybrid Quantum Networks (Hy-Q).

Continue reading “Major Computing Breakthrough: Copenhagen Researchers Can Now Achieve “Quantum Advantage”” | >

The first step is to understand qubits and superposition. The next one is to get a handle on the business advantage that this technology represents.

If “figure out quantum computing” is still in your future file, it’s time to update your timeline. The industry is nearing the end of the early adopter phase, according to one expert, and the time is now to get up to speed.

Denise Ruffner, the vice president of business development at IonQ, said that quantum computing is evolving much faster than many people realize.

Continue reading “To do in 2021: Get up to speed with quantum computing 101” | >

JILA physicists have boosted the signal power of their atomic “tweezer clock” and measured its performance in part for the first time, demonstrating high stability close to the best of the latest generation of atomic clocks.

The unusual clock, which uses to trap, control and isolate , offers unique possibilities for enhancing clock performance using the tricks of quantum physics as well as future applications in quantum information processing, , and measurement science.

Described in a Nature paper published online Dec. 16, the clock platform is a rectangular grid of about 150 strontium atoms confined individually by , which are created by a aimed through a microscope and deflected into 320 spots. This upgraded version of the clock has up to 30 times as many atoms as the preliminary design unveiled last year, due mainly to the use of several different lasers, including a green one for trapping the atoms and two red ones to make them “tick.”

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A new study illuminates surprising choreography among spinning atoms. In a paper appearing in the journal Nature, researchers from MIT and Harvard University reveal how magnetic forces at the quantum, atomic scale affect how atoms orient their spins.

In experiments with ultracold lithium , the researchers observed different ways in which the spins of the atoms evolve. Like tippy ballerinas pirouetting back to upright positions, the spinning atoms return to an equilibrium orientation in a way that depends on the between individual atoms. For example, the atoms can spin into equilibrium in an extremely fast, “ballistic” fashion or in a slower, more diffuse pattern.

The researchers found that these behaviors, which had not been observed until now, could be described mathematically by the Heisenberg model, a set of equations commonly used to predict magnetic behavior. Their results address the fundamental nature of magnetism, revealing a diversity of behavior in one of the simplest magnetic materials.

Continue reading “Ultracold atoms reveal a new type of quantum magnetic behavior” | >

More than two-thirds of the energy used worldwide is ultimately ejected as “waste heat.” Within that reservoir of discarded energy lies a great and largely untapped opportunity, claim scientists in MIT’s Department of Nuclear Science and Engineering (NSE). As reported in a recent issue of Nature Communications, the MIT team—led by Assistant Professor Mingda Li, who heads NSE’s Quantum Matter Group—has achieved a breakthrough in thermoelectric generation, which offers a direct means of converting thermal energy, including waste heat, into electricity.

A , or difference, within a material such as a metal or semiconductor can, through a phenomenon known as the Seebeck effect, give rise to an that drives a current. “For many materials, the is too low to be useful,” explains NSE Research Scientist Fei Han. “Our goal is to find materials with conversion efficiencies high enough to make thermoelectric generation more practical.”

The efficiency of thermoelectric energy conversion is proportional to a material’s , electrical , and something called the “” squared; it is inversely proportional to the . Because efficiency goes up with temperature, most thermoelectric materials used today operate in the range of hundreds of degrees centigrade. “But in our lives, most of the stuff around us is at room temperature,” Han says. “That’s why we’re trying to discover new materials that work effectively at or below room temperature.”

Continue reading “A cool advance in thermoelectric conversion” | >

Since the very beginning of quantum physics, a hundred years ago, it has been known that all particles in the universe fall into two categories: fermions and bosons. For instance, the protons found in atomic nuclei are fermions, while bosons include photons — which are particles of light — as well as the BroutEnglert-Higgs boson, for which Francois Englert, a professor at ULB, was awarded a Nobel Prize in Physics in 2013.

Bosons — especially photons — have a natural tendency to clump together. One of the most remarkable experiments that demonstrated photons’ tendency to coalesce was conducted in 1987, when three physicists identified an effect that was since named after them: the Hong-Ou-Mandel effect. If two photons are sent simultaneously, each towards a different side of a beam splitter — a sort of semitransparent mirror — one could expect that each photon will be either reflected or transmitted.

Logically, photons should sometimes be detected on opposite sides of this mirror, which would happen if both are reflected or if both are transmitted. However, the experiment has shown that this never actually happens: the two photons always end up on the same side of the mirror, as though they ‘preferred’ sticking together! In an article published recently in US journal Proceedings of the National Academy of Sciences, Nicolas Cerf — a professor at the Centre for Quantum Information and Communication (École polytechnique de Bruxelles) — and his former PhD student Michael Jabbour — now a postdoctoral researcher at the University of Cambridge — describe how they identified another way in which photons manifest their tendency to stay together. Instead of a semi-transparent mirror, the researchers used an optical amplifier, called an active component because it produces new photons.

Continue reading “Quantum Interference Phenomenon Identified That Occurs Through Time” | >
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