Related Experiment Video
Updated: Nov 27, 2025
06:42
Generation and Coherent Control of Pulsed Quantum Frequency Combs
Published on: June 8, 2018
9.4K
Quantifying the Unitary Generation of Coherence from Thermal Quantum Systems.
Shimshon Kallush1,2, Aviv Aroch2, Ronnie Kosloff2
1Department of Physics and Optical Engineering, ORT-Braude College, 21982 Karmiel, Israel.
Entropy (Basel, Switzerland)
|December 3, 2020
Summary
Researchers explored generating quantum coherence from thermal states using external fields. Maximum coherence is achieved with specific energy distributions, avoiding suboptimal traps when energy constraints are carefully managed.
Area of Science:
- Quantum mechanics
- Quantum information theory
Background:
- Coherence is a key feature of transient quantum states.
- Equilibrium thermal quantum systems lack coherence.
Purpose of the Study:
- Investigate generating maximum quantum coherence from an initial thermal state.
- Utilize external fields for quantum control.
Main Methods:
- Assumed a completely controllable Hamiltonian for all unitary transformations.
- Optimized unitary control to achieve maximum coherence.
- Analyzed energy distributions under different constraints.
Main Results:
- Maximum coherence resulted in a micro-canonical energy distribution without energy constraints.
- Constraining energy led to a canonical energy population distribution.
- Local suboptimal traps were found with tight energy constraints; global optimum achieved with a small Lagrange multiplier.
Conclusions:
- Demonstrated a control scenario to generate maximum coherence from a thermal state.
- The optimization task is generally trap-less, but energy constraints can introduce traps.
- Exploring coherence generation near the density matrix diagonal is a future direction.
Related Concept Videos
02:46Quantifying Heat
60.4K
Thermal Energy Microscopically, thermal energy is the kinetic energy associated with the random motion of atoms and molecules. Temperature is a quantitative measure of “hot” or “cold”, which depends on the amount of thermal energy. When the atoms and molecules in an object are moving or vibrating quickly, they have a higher average kinetic energy (KE) (or higher thermal energy), and the object is perceived as “hot”, or it is described as being at a higher temperature. When the...
60.4K
01:14Zeroth Law of Thermodynamics
6.4K
Experimentally, if object A is in equilibrium with object B, and object B is in equilibrium with object C, then object A is in equilibrium with object C. That statement of transitivity is called the "zeroth law of thermodynamics." For example, a cold metal block and a hot metal block are both placed on a metal plate at room temperature. Eventually, the cold block and the plate will be in thermal equilibrium. In addition, the hot block and the plate will be in thermal equilibrium.
6.4K
01:15Statements of the Second Law of Thermodynamics
4.7K
The second law of thermodynamics can be stated in several different ways, and all of them can be shown to imply the others. The Clausius’ statement of the second law of thermodynamics is based on the irreversibility of spontaneous heat flow. It states that heat will not flow from the colder body to the hotter body unless some other process is involved. Additionally, as per the Kelvin’s statement, it is impossible to convert the heat from a single source into work without any other...
4.7K
01:20Entropy and the Second Law of Thermodynamics
4.0K
The second law of thermodynamics can be stated quantitatively using the concept of entropy. Entropy is the measure of disorder of the system.
The relation between entropy and disorder can be illustrated with the example of the phase change of ice to water. In ice, the molecules are located at specific sites giving a solid state, whereas, in a liquid form, these molecules are much freer to move. The molecular arrangement has therefore become more randomized. Although the change in average...
The relation between entropy and disorder can be illustrated with the example of the phase change of ice to water. In ice, the molecules are located at specific sites giving a solid state, whereas, in a liquid form, these molecules are much freer to move. The molecular arrangement has therefore become more randomized. Although the change in average...
4.0K
01:24Thermodynamics: Activity Coefficient
2.5K
Activity is the measure of the effective concentration of the species in solution. It can be expressed as the product of the molar concentration of the species and its activity coefficient. The activity coefficient is a dimensionless quantity and depends on the total ionic strength of the solution.
The activity coefficient is a measure of the deviation from ideal behavior. When the ionic strength of the solution is minimal, the activity coefficient of an ionic species is close to unity, making...
The activity coefficient is a measure of the deviation from ideal behavior. When the ionic strength of the solution is minimal, the activity coefficient of an ionic species is close to unity, making...
2.5K
01:21Energy Associated With a Charge Distribution
1.8K
The work done to bring a charge through a distance r is given by the potential difference between the initial and the final position. To assemble a collection of point charges, the total work done can be expressed in terms of the product of each pair of charges divided by their separation distance, defined with respect to a suitable origin. Solving this expression gives the energy stored in a point charge distribution.
1.8K