How are computational basis states represented at the hardware level? Is there some energy level distinction?

[quantumadmin]

Question - How are computational basis states represented at the hardware level? Is there some energy level distinction between them to distinguish them? For n unentangled but superposed qubits with 2^n distinct states, how are each of those distinct 2^n computational basis states distinguished from each other, at the hardware level? If not an energy or mass distinction between the states, what is different between them, at the hardware level?

Answer -

At the hardware level in quantum computing, computational basis states are typically represented using different quantum states of physical qubits. The distinction between these states is not based on energy levels or mass, but rather on the quantum properties of the physical system being used to implement the qubits.

The most common physical systems used for qubits include superconducting circuits, trapped ions, and topological qubits. Each of these systems has its own way of representing and distinguishing computational basis states.

Superconducting Qubits:
In superconducting qubits, the computational basis states are typically represented by different charge or flux states of superconducting circuits. These circuits consist of Josephson junctions, which can exhibit quantized energy levels. The qubits are manipulated using microwave pulses that drive transitions between these energy levels, allowing for coherent superpositions and entanglement.

Trapped Ion Qubits:
Trapped ion qubits use the internal energy levels of individual ions to represent qubit states. The qubits are encoded in the internal electronic states of ions, and laser beams are used to manipulate these states and create superpositions and entanglement.

Topological Qubits:
Topological qubits, which are still under research and development, aim to use exotic states of matter to create robust qubits. These qubits would rely on topological properties of materials that can be manipulated to encode and manipulate quantum information.

The distinction between the 2^n distinct computational basis states for n unentangled but superposed qubits is achieved through careful control of the physical qubit states and their interactions. It involves manipulating the quantum states of individual qubits using gates and interactions that correspond to quantum logic operations.

At the hardware level, qubits are typically operated at extremely low temperatures (close to absolute zero) to minimize decoherence and maintain the quantum properties necessary for computation. The differences between the computational basis states are manifested through the quantum states of the physical qubits, which can be accessed and manipulated using appropriate control mechanisms, such as microwave pulses or laser beams, depending on the qubit technology.

In summary, the distinction between computational basis states in quantum computing hardware is not based on energy or mass differences, but rather on the unique quantum properties and interactions of the physical qubits used to implement the quantum information. The ability to manipulate and distinguish these states accurately is crucial for performing quantum computations.