MIT News September 25, 2018 Extreme sensitivity of quantum sensors to their surrounding environment creates the vexing problem of environmental noise in quantum sensor systems. A team of researchers in the US (MIT, Yale University) has developed an approach that is complementary to existing Dynamical decoupling and established error-corrected quantum sensing (ECQS) methods. This approach allows frequency-independent filtering, because it exploits spatial rather than temporal noise correlations. The new ECQS scheme makes use of noise correlations at different positions in a quantum sensor. In this way, the new approach can tell signal from noise even in the common case where […]
Category Archives: Quantum science
Searching for errors in the quantum world
Science Daily September 18, 2018 Many scientists dream of combining quantum mechanics with the theory of relativity to form a coherent worldview. As actually experiments are not possible, researchers in Switzerland propose a thought experiment to investigate the question whether quantum theory can, in principle, have universal validity. The idea is that, if the answer was yes, it must be possible to employ quantum theory to model complex systems that include agents which are themselves using quantum theory. Analysing the experiment under this presumption, they found that one agent, upon observing a particular measurement outcome, must conclude that another agent […]
Efficient generation of photon pairs from modified carbon nanotubes
Physics News September 6, 2018 Doping SWCNTs is emerging as an effective means for enhancing the emission properties of nanotubes and introducing new functionalities. Researchers at Los Alamos National Laboratory showed that the photon pair emission originates from two successive captures and recombination of excitons at a solitary oxygen dopant state and this type of photon pair emission process can happen at an efficiency as high as 44 percent of the single photon emission. The main limiting factor for the efficiency of this process is exciton-exciton annihilation. This work opens an exciting new path toward carbon nanotube-based lasers and entangled […]
Physicists implement a version of Maxwell’s famous thought experiment for reducing entropy
Phys.org September 8, 2018 Reduced entropy in a three-dimensional lattice of super-cooled, laser-trapped atoms could help speed progress toward creating quantum computers. Researchers at Pennsylvania State University rearranged a randomly distributed array of atoms into neatly organized blocks, thus performing the function of a “Maxwell’s demon”—a thought experiment from the 1870s that challenged the second law of thermodynamics. The organized blocks of atoms could form the basis for a quantum computer that uses uncharged atoms to encode data and perform calculations… read more. TECHNICAL ARTICLE
D-Wave demonstrates first large-scale quantum simulation of topological state of matter
Eurekalert August 22, 2018 Researchers in Canada demonstrated a large-scale quantum simulation of this phenomenon in a network of 1,800 in situ programmable superconducting niobium flux qubits whose pairwise couplings are arranged in a fully frustrated square-octagonal lattice. They observed the emergence of a complex order parameter with continuous rotational symmetry, and the onset of quasi-long-range order as the system approaches a critical temperature. According to the researchers the approach of using a quantum processor as a programmable magnetic lattice will find widespread use in the simulation and development of exotic materials…read more. TECHNICAL ARTICLE
Novel approach to coherent control of a three-level quantum system
Science Daily August 8, 2018 Researchers in Switzerland combined a quantum system with a mechanical oscillator employing electrons trapped in nitrogen-vacancy centers and embedded these spins in single-crystalline mechanical resonators made from diamond. The nitrogen-vacancy spins possess three eigenstates, which can be described as “up,” “down” and “zero.” The researchers showed complete quantum control over such a three-level system, in a way not possible before. They showed that if the three eigenstates are coupled to each other the coherence time can be significantly extended. Research could have application in quantum sensing or quantum information processing… read more. Open Access TECHNICAL […]
Reversing cause and effect is no trouble for quantum computers
Phys.org July 20, 2018 When physics does not impose any direction on time, where does causal asymmetry—the memory overhead needed to reverse cause and effect—come from? An international team of researchers (Singapore, UC Davis, UK, Austria) has shown that quantum models forced to run in the less-natural temporal direction not only surpass their optimal classical counterparts but also any classical model running in reverse time. This holds even when the memory overhead is unbounded, resulting in quantum models with unbounded memory advantage. According to the researchers the models that use quantum physics can entirely mitigate the memory overhead. Doing away […]
Physicists show that is impossible to mask quantum information in correlations
Phys.org June 21 2018 Classical information encoded in composite quantum states can be completely hidden from the reduced subsystems and may be found only in the correlations. An international team of researchers (Australia, India) has shown that while this may still be true for some restricted sets of nonorthogonal quantum states, it is not possible for arbitrary quantum states. This result suggests that quantum qubit commitment—a stronger version of the quantum bit commitment—is not possible in general. The findings may have potential applications in secret sharing and future quantum communication protocols…read more. TECHNICAL ARTICLE
Environmental noise paradoxically preserves the coherence of a quantum system
Phys.org May 30, 2018 Normally dephasing causes decoherence in quantum systems. An international team of researchers (Japan, Germany, USA – University of Buffalo, University of Michigan) shows a scheme of entanglement engineering where pure dephasing assists the generation of quantum entanglement at distant sites in a chain of electron spins confined in semiconductor quantum dots. One party of an entangled spin pair, prepared at a single site, is transferred to the next site and then adiabatically swapped with a third spin using a transition across a multi-level avoided crossing. This process is accelerated by the noise-induced dephasing… read more. Open […]
How can you tell if a quantum memory is really quantum?
Phys.org May 23, 2018 Often it is difficult to tell whether a memory is storing quantum or merely classical information. The new test developed by an international team of researchers (Taiwan, Switzerland, Japan, Canada) uses a semiquantum framework that is very similar to that used in some tests of entanglement. By comparing the relative frequencies of the sent and received signals it is possible to estimate the time-like entanglement and therefore certify that a quantum memory can store quantum information. They showed that the new test is robust against noise and losses, and they expect that it should be possible […]