82 research outputs found

### Learn Quantum Mechanics with Haskell

To learn quantum mechanics, one must become adept in the use of various
mathematical structures that make up the theory; one must also become familiar
with some basic laboratory experiments that the theory is designed to explain.
The laboratory ideas are naturally expressed in one language, and the
theoretical ideas in another. We present a method for learning quantum
mechanics that begins with a laboratory language for the description and
simulation of simple but essential laboratory experiments, so that students can
gain some intuition about the phenomena that a theory of quantum mechanics
needs to explain. Then, in parallel with the introduction of the mathematical
framework on which quantum mechanics is based, we introduce a calculational
language for describing important mathematical objects and operations, allowing
students to do calculations in quantum mechanics, including calculations that
cannot be done by hand. Finally, we ask students to use the calculational
language to implement a simplified version of the laboratory language, bringing
together the theoretical and laboratory ideas.Comment: In Proceedings TFPIE 2015/6, arXiv:1611.0865

### Learn Physics by Programming in Haskell

We describe a method for deepening a student's understanding of basic physics
by asking the student to express physical ideas in a functional programming
language. The method is implemented in a second-year course in computational
physics at Lebanon Valley College. We argue that the structure of Newtonian
mechanics is clarified by its expression in a language (Haskell) that supports
higher-order functions, types, and type classes. In electromagnetic theory, the
type signatures of functions that calculate electric and magnetic fields
clearly express the functional dependency on the charge and current
distributions that produce the fields. Many of the ideas in basic physics are
well-captured by a type or a function.Comment: In Proceedings TFPIE 2014, arXiv:1412.473

### Maximum stabilizer dimension for nonproduct states

Composite quantum states can be classified by how they behave under local
unitary transformations. Each quantum state has a stabilizer subgroup and a
corresponding Lie algebra, the structure of which is a local unitary invariant.
In this paper, we study the structure of the stabilizer subalgebra for n-qubit
pure states, and find its maximum dimension to be n-1 for nonproduct states of
three qubits and higher. The n-qubit Greenberger-Horne-Zeilinger state has a
stabilizer subalgebra that achieves the maximum possible dimension for pure
nonproduct states. The converse, however, is not true: we show examples of pure
4-qubit states that achieve the maximum nonproduct stabilizer dimension, but
have stabilizer subalgebra structures different from that of the n-qubit GHZ
state.Comment: 6 page

### Werner state structure and entanglement classification

We present applications of the representation theory of Lie groups to the
analysis of structure and local unitary classification of Werner states,
sometimes called the {\em decoherence-free} states, which are states of $n$
quantum bits left unchanged by local transformations that are the same on each
particle. We introduce a multiqubit generalization of the singlet state, and a
construction that assembles these into Werner states.Comment: 9 pages, 2 figures, minor changes and corrections for version

### Classification of nonproduct states with maximum stabilizer dimension

Nonproduct n-qubit pure states with maximum dimensional stabilizer subgroups
of the group of local unitary transformations are precisely the generalized
n-qubit Greenberger-Horne-Zeilinger states and their local unitary equivalents,
for n greater than or equal to 3 but not equal to 4. We characterize the Lie
algebra of the stabilizer subgroup for these states. For n=4, there is an
additional maximal stabilizer subalgebra, not local unitary equivalent to the
former. We give a canonical form for states with this stabilizer as well.Comment: 6 pages, version 3 has a typographical correction in the displayed
equation just after numbered equation (2), and other minor correction

### Symmetric mixed states of $n$ qubits: local unitary stabilizers and entanglement classes

We classify, up to local unitary equivalence, local unitary stabilizer Lie
algebras for symmetric mixed states into six classes. These include the
stabilizer types of the Werner states, the GHZ state and its generalizations,
and Dicke states. For all but the zero algebra, we classify entanglement types
(local unitary equivalence classes) of symmetric mixed states that have those
stabilizers. We make use of the identification of symmetric density matrices
with polynomials in three variables with real coefficients and apply the
representation theory of SO(3) on this space of polynomials.Comment: 10 pages, 1 table, title change and minor clarifications for
published versio

### Classification of n-qubit states with minimum orbit dimension

The group of local unitary transformations acts on the space of n-qubit pure
states, decomposing it into orbits. In a previous paper we proved that a
product of singlet states (together with an unentangled qubit for a system with
an odd number of qubits) achieves the smallest possible orbit dimension, equal
to 3n/2 for n even and (3n + 1)/2 for n odd, where n is the number of qubits.
In this paper we show that any state with minimum orbit dimension must be of
this form, and furthermore, such states are classified up to local unitary
equivalence by the sets of pairs of qubits entangled in singlets.Comment: 15 pages, latex, revision 2, conclusion added, some proofs shortene

### Multiparty quantum states stabilized by the diagonal subgroup of the local unitary group

We classify, up to local unitary equivalence, the set of $n$-qubit states
that is stabilized by the diagonal subgroup of the local unitary group. We
exhibit a basis for this set, parameterized by diagrams of nonintersecting
chords connecting pairs of points on a circle, and give a criterion for when
the stabilizer is precisely the diagonal subgroup and not larger. This
investigation is part of a larger program to partially classify entanglement
type (local unitary equivalence class) via analysis of stabilizer structure.Comment: 4 pages, 3 figures. Version 2 has numerous small changes and
correction

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