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Category: quantum physics – Page 660

Weird quantum objects known as Q balls could explain why we exist

Theoretical “lumps” called Q balls formed in the moments after the Big Bang.

One of the biggest cosmological mysteries is why the universe is made up of way more matter than antimatter, essentially why we exist. Now, a team of theoretical physicists says they know how to find the answer. All they need to do is detect the gravitational waves produced by bizarre quantum objects called Q balls.

Every kind of ordinary matter particle has an antimatter partner with opposing characteristics — and when matter interacts with antimatter, the two annihilate each other. That fact makes our existence a mystery, as cosmologists are pretty sure that at the dawn of the universe, equal amounts of matter and antimatter were produced; those matter and antimatter partners should have all annihilated each other, leaving the universe devoid of any matter at all. Yet matter exists, and researchers are slowly uncovering the reasons why.

Mini course on “What is Computation? From Turing Machines to Blackholes and Neurons” — guest post

[Cross posted on Chi-Ning’s blog, the course is open also to non-Harvard people. Chi-Ning is my amazing grad student, who has worked on several aspects related to the course, including quantum computation and neurally-plausible computation. He assembled a great collection of guest speakers and so this course looks like it will be very exciting. Boaz]

In the following January, Harvard GSAS kindly supports me to offer a mini-course on “What is Computation? From Turing Machines to Blackholes and Neurons”. In this blog post, I’m going to share the motivation for teaching this mini-course and give an overview on what you will learn if you are interested in participating!

Computation is not an exotic word for people living in the 21st century. In high school, kids have to learn and do all sorts of computations in arithmetics (and some even start to write computer programs!). For scientists, computational methods become more and more common and sometimes even completely change the paradigm of a field. There are computers of different forms hiding in our daily life ranging from your smartphones to the toy of your pets. Also, from time to time we see excitement on the news about the development of quantum computing and artificial intelligence. Computation has become central in human civilization, however, do we really understand what computation is?

Important Milestone Reached in Quantum Computing With Error Correction

“Until now researchers have encoded and stabilized. We now show that we can compute as well.”

Researchers at QuTech—a collaboration between the TU Delft and TNO—have reached a milestone in quantum error correction. They have integrated high-fidelity operations on encoded quantum data with a scalable scheme for repeated data stabilization. The researchers report their findings in the December issue of Nature Physics.

Physical quantum bits, or qubits, are vulnerable to errors. These errors arise from various sources, including quantum decoherence, crosstalk, and imperfect calibration. Fortunately, the theory of quantum error correction stipulates the possibility to compute while synchronously protecting quantum data from such errors.

Proposal for an experimental test of the many-worlds interpretation of quantum mechanics

The many-worlds interpretation of quantum mechanics predicts the formation of distinct parallel worlds as a result of a quantum mechanical measurement. Communication among these parallel worlds would experimentally rule out alternatives to this interpretation. A procedure for “interworld’’ exchange of information and energy, using only state of the art quantum optical equipment, is described. A single ion is isolated from its environment in an ion trap. Then a quantum mechanical measurement with two discrete outcomes is performed on another system, resulting in the formation of two parallel worlds. Depending on the outcome of this measurement the ion is excited from only one of the parallel worlds before the ion decoheres through its interaction with the environment. A detection of this excitation in the other parallel world is direct evidence for the many-worlds interpretation.

Beyond Qubits: Unlocking the Third State in Quantum Processors

By Alex Hill, Senior Quantum Systems Engineer

Qubits are the basic building block of a quantum processor, and are so named because they represent a continuum of complex superpositions of two basic quantum states. The power of qubits comes in part from their ability to encode significantly more information than a classical bit — an infinite set of states between 0 and 1. In mathematical terms, quantum gates that manipulate the state of individual qubits are unitary operators drawn from SU.

Rigetti’s superconducting quantum processors are based on the transmon design [1]. Each physical qubit is an anharmonic oscillator, meaning that the energy gaps between subsequent qubit energy states decrease as the qubit climbs higher up the state ladder. We typically only address the first two states, 0 and 1 (in the literature, sometimes referred to as g(round) and e(xcited)); however, the design of our qubits supports even higher states. The simple structure of the transmon energy levels gives superconducting qubits the unique ability to address many of these states in a single circuit.

Two-time interpretation of quantum mechanics

We suggest an interpretation of quantum mechanics, inspired by the ideas of Aharonov et al. of a time-symmetric description of quantum theory. We show that a special final boundary condition for the Universe, may be consistently defined as to determine single classical-like measurement outcomes, thus solving the “measurement problem”. No other deviation is made from standard quantum mechanics, and the resulting theory is deterministic (in a two-time sense) and local. Quantum mechanical probabilities are recovered in general, but are eliminated from the description of any single measurement. We call this the Two-time interpretation of quantum mechanics. We analyze ideal measurements, showing how the quantum superposition is, in effect, dynamically reduced to a single classical state via a “two-time decoherence” process.

The Two-State Vector Formalism of Qauntum Mechanics: an Updated Review

In this paper we present the two-state vector formalism of quantum mechanics. It is a time-symmetrized approach to standard quantum theory particularly helpful for the analysis of experiments performed on pre-and post-selected ensembles. Several peculiar effects which naturally arise in this approach are considered. In particular, the concept of “weak measurements’’ (standard measurements with weakening of the interaction) is discussed in depth revealing a very unusual but consistent picture. Also, a design of a gedanken experiment which implements a kind of quantum “time machine’’ is described. The issue of time-symmetry in the context of the two-state vector formalism is clarified.

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