Best Ground State

A density matrix describes the state of a quantum system, even when that state is unknown or entangled, by representing probabilities across possible pure states and their mixtures.

The Bloch sphere is a geometrical representation of a qubit's state, visualizing its superposition as a point on the surface of a unit sphere where axes represent classical bit values (0 and 1).

A Greenberger–Horne–Zeilinger (GHZ) state is a specific entangled quantum state of three or more particles where measuring the properties of one instantaneously influences the possible outcomes for all others, regardless of distance.

A coherent state is a specific quantum state of a harmonic oscillator exhibiting properties remarkably similar to classical expectations, minimizing uncertainty between position and momentum.

The Wigner function represents a quasi-probability distribution in phase space, offering a way to analyze quantum states by mapping them onto a classical-like representation despite not always being positive.

A squeezed state is a quantum mechanical state where the uncertainty in one observable, like position or momentum, is reduced below the standard limit allowed by the Heisenberg principle, at the expense of increased uncertainty in the complementary variable.

Cat state, derived from Schrödinger's thought experiment, describes a quantum system existing in multiple contradictory states simultaneously—like a cat being both alive and deceased—until measured.

Zero-point energy describes the lowest possible energy state of a quantum mechanical system; even at absolute zero temperature, fluctuations persist due to the Heisenberg uncertainty principle.

A Fock state in quantum mechanics represents a specific, well-defined eigenstate of the number operator, signifying a fixed and known number of particles occupying particular energy levels within a system.

The Husimi Q function, a quasiprobability distribution in quantum mechanics, smooths the Wigner function to ensure non-negativity, representing a mixed state as a "fuzzy" phase space density.

A qudit is a generalization of the qubit, representing a quantum system with *d* possible states—where *d* is an integer greater than or equal to two—and enabling richer computational possibilities than qubits alone.

A qutrit is a quantum bit that can exist in three distinct states—analogous to the binary 0 and 1 of classical bits—allowing for potentially greater computational possibilities than qubits.

NOON states are entangled quantum systems where both possibilities of a property (like spin) exist simultaneously until measurement forces one outcome, unlike classical certainty.