Quantum Technology

Quantum technology uses the principles of quantum physics to create devices and systems with capabilities that cannot be fully explained using classical physics alone.

Quantum physics describes the behaviour of:

• atoms
• electrons
• photons
• nuclei
• other microscopic particles

Many technologies that are now part of everyday life already depend on quantum physics, including:

• lasers
• transistors
• computer chips
• LEDs
• solar cells
• medical imaging systems
• atomic clocks

A newer generation of technologies deliberately controls quantum effects such as superposition, entanglement and tunneling to create quantum computers, quantum sensors and quantum communication systems.

---

From Quantum Physics to Technology

Quantum physics developed because classical physics could not explain several experimental observations.

Important quantum ideas include:

• quantized energy levels
• photons
• wave-particle duality
• matter waves
• quantum tunneling
• superposition
• uncertainty
• entanglement

These ideas initially seemed highly theoretical.

Today they form the foundation of enormous parts of modern technology.

A useful distinction is between:

first-generation quantum technologies

and:

second-generation quantum technologies

---

First-Generation Quantum Technologies

These technologies use quantum effects but do not usually require scientists to control individual quantum states.

Examples include:

• lasers
• transistors
• semiconductor chips
• LEDs
• solar cells
• magnetic resonance technologies
• atomic clocks

These technologies already have enormous economic and scientific importance.

---

Emerging Quantum Technologies

Newer quantum technologies attempt to deliberately create, control and measure individual quantum states.

Examples include:

• quantum computers
• quantum communication
• quantum cryptography
• quantum sensors
• quantum simulators
• quantum networks

These technologies rely heavily on effects such as:

superposition

and:

entanglement

---

Quantized Energy Levels

One of the most important ideas behind quantum technology is that atoms do not possess arbitrary electron energies.

Electrons occupy:

quantized energy states

When an electron moves between energy levels, energy is absorbed or emitted.

For a photon:

ΔE = hf

where:

• ΔE = difference between energy levels
• h = Planck's constant
• f = photon frequency

Therefore, the energy-level structure of matter determines the wavelengths of light that can be absorbed or emitted.

This principle is fundamental to:

• lasers
• LEDs
• spectroscopy
• photodetectors

---

Lasers

LASER stands for:

Light Amplification by Stimulated Emission of Radiation

A laser produces an intense, highly controlled beam of light.

Laser operation depends directly on quantum energy levels and the interaction between photons and atoms.

---

Absorption

Suppose an atom has a lower energy state E₁ and a higher state E₂.

If a photon has exactly the appropriate energy:

hf = E₂ − E₁

the atom can absorb the photon.

The electron moves to a higher-energy state.

This is:

absorption

---

Spontaneous Emission

An excited atom is unstable.

Eventually it may return to a lower-energy state and emit a photon.

The photon energy is:

hf = E₂ − E₁

This process is called:

spontaneous emission

The emitted photon can travel in a random direction.

---

Stimulated Emission

Einstein showed that an incoming photon can stimulate an excited atom to emit another photon.

The new photon has the same:

• frequency
• phase
• direction
• polarization

as the stimulating photon.

This process is called:

stimulated emission

It is the central quantum process behind laser operation.

---

Population Inversion

Normally, more atoms occupy low-energy states than high-energy states.

For laser amplification, scientists create a:

population inversion

This means:

more particles occupy the relevant excited state than the lower state

Energy must be supplied to the laser medium to produce this condition.

This process is called:

pumping

---

The Laser Cavity

A typical laser contains:

• gain medium
• energy source
• two mirrors

Photons travel back and forth between the mirrors.

As they pass through the gain medium, they stimulate additional photon emission.

One mirror is partially transmitting.

Some light escapes through this mirror as the:

laser beam

---

Properties of Laser Light

Laser light has several useful characteristics.

It is often highly:

monochromatic

meaning it contains a narrow range of wavelengths.

It is highly:

coherent

meaning the light waves maintain well-defined phase relationships.

It is also strongly:

directional

so the beam spreads relatively little.

These properties make lasers useful for precise measurements and communication.

---

Applications of Lasers

Lasers are used in:

• fibre-optic communication
• barcode scanners
• laser printers
• manufacturing
• cutting and welding
• eye surgery
• medical treatment
• scientific research
• spectroscopy
• surveying
• optical storage
• distance measurement

Quantum physics therefore has direct applications throughout modern society.

---

Semiconductors

A semiconductor is a material whose electrical behaviour lies between that of a conductor and an insulator.

The most important semiconductor material in modern electronics is:

silicon

Semiconductors form the basis of:

• transistors
• integrated circuits
• computer processors
• LEDs
• solar cells
• sensors

Understanding semiconductors requires quantum physics.

---

Energy Bands

In an isolated atom, electrons occupy discrete energy levels.

When enormous numbers of atoms form a solid, these levels combine into ranges called:

energy bands

Two particularly important bands are:

valence band

and:

conduction band

Between them is the:

band gap

---

The Band Gap

Electrons in the valence band are generally associated with bonding within the material.

Electrons in the conduction band can move more freely through the material and contribute to electrical current.

For conduction to occur, electrons may need enough energy to cross the:

band gap

Semiconductors have a moderate band gap.

This allows their conductivity to be carefully controlled.

---

Doping Semiconductors

The electrical properties of semiconductors can be modified by adding small amounts of other elements.

This process is called:

doping

Doping can produce:

n-type semiconductor

or:

p-type semiconductor

---

n-Type Semiconductors

An n-type semiconductor contains additional electrons that can contribute to conduction.

Its majority charge carriers are:

electrons

---

p-Type Semiconductors

A p-type semiconductor contains vacancies in electron states called:

holes

A hole behaves effectively like a positive charge carrier.

Its majority charge carriers are:

holes

---

The p-n Junction

When p-type and n-type semiconductor materials are joined, they form a:

p-n junction

This structure is fundamental to many electronic devices.

Applications include:

• diodes
• LEDs
• solar cells
• transistors

Quantum physics explains the energy states and charge-carrier behaviour that make these devices possible.

---

Transistors

The transistor is one of the most important inventions in modern technology.

A transistor can act as:

• an electronic switch
• an amplifier

Digital computers use enormous numbers of microscopic transistors to represent and process binary information.

---

From Transistors to Computers

Digital electronics represent information using states such as:

0

and:

1

Transistors can switch electrical signals between different states.

Billions of transistors can be placed on a modern integrated circuit.

Therefore:

quantum physics → semiconductor physics → transistor → integrated circuit → modern computer

Much of the digital world depends indirectly on quantum theory.

---

Light-Emitting Diodes

An LED converts electrical energy into light.

Electrons transition between energy states in a semiconductor and release energy as photons.

Approximately:

ΔE = hf

The size of the semiconductor band gap influences the photon frequency and therefore the emitted colour.

LEDs demonstrate a direct connection between:

quantum energy levels and everyday technology

---

Solar Cells

Solar cells perform essentially the reverse energy conversion.

Photons are absorbed by semiconductor materials.

Their energy can promote electrons into higher-energy states.

The resulting charge carriers can produce:

electric current

Solar energy technology therefore depends strongly on quantum and semiconductor physics.

---

Quantum Tunneling in Technology

Quantum tunneling allows particles to cross barriers that would be forbidden classically.

Tunneling is used in technologies such as:

• scanning tunneling microscopes
• tunnel diodes
• some memory technologies
• Josephson junctions

It is also an important consideration in extremely small semiconductor devices.

As electronic components shrink, unwanted electron tunneling can create:

leakage currents

---

Scanning Tunneling Microscopes

A scanning tunneling microscope (STM) uses quantum tunneling to investigate conducting surfaces at extremely small scales.

An extremely sharp tip is placed close to a surface.

Electrons tunnel through the tiny gap.

The tunneling current depends extremely strongly on the:

tip-surface distance

By measuring this current while scanning the tip, scientists can map surface features at atomic scales.

---

Atomic Clocks

Quantum physics also allows extremely precise measurement of:

time

Atomic clocks use specific transitions between quantum energy states in atoms.

Because these transition frequencies are extremely stable, they provide highly precise frequency references.

Atomic clocks are essential for:

• global navigation satellite systems
• telecommunications
• scientific measurements
• synchronization of networks

---

Why GPS Needs Atomic Clocks

Navigation systems determine position using extremely precise timing.

Electromagnetic signals travel approximately:

300,000 km each second

A timing error of only:

1 microsecond

corresponds to a distance error of roughly:

300 m

Extremely accurate clocks are therefore essential for precise navigation.

Quantum transitions provide the required stability.

---

Quantum Sensors

A quantum sensor uses quantum phenomena to make extremely sensitive measurements.

Quantum sensors can measure quantities such as:

• magnetic fields
• acceleration
• gravity
• time
• electric fields

Possible applications include:

• medical imaging
• geological exploration
• navigation
• fundamental physics
• detecting underground structures
• monitoring Earth's magnetic field

---

Quantum Communication

Quantum physics can also be used to transmit information.

An important emerging field is:

quantum communication

Quantum communication may use individual photons and quantum states to transmit or protect information.

One major application is:

quantum key distribution

or:

QKD

---

Quantum Key Distribution

QKD allows two parties to establish cryptographic key material using quantum states.

The important principle is that measuring an unknown quantum state can disturb it.

Therefore, under suitable protocols, attempts to intercept the quantum signals can produce detectable changes.

This can help reveal:

eavesdropping

QKD does not mean every part of communication automatically becomes perfectly secure; the complete system and its implementation still matter.

---

Quantum Entanglement

One of the most unusual quantum phenomena is:

entanglement

Two quantum systems can share a joint state such that their measurement outcomes have correlations that cannot be reproduced by simple classical local models.

Entanglement is an important resource in:

• quantum computing
• quantum communication
• quantum sensing
• quantum networks

It does not allow usable information to be transmitted faster than light.

---

Quantum Superposition

A classical bit has one definite state:

0 or 1

A quantum system can be prepared in a:

superposition

of basis states.

For a quantum bit:

|ψ⟩ = α|0⟩ + β|1⟩

where α and β are probability amplitudes.

The probabilities of measurement outcomes are related to:

|α|² and |β|²

with:

|α|² + |β|² = 1

---

Qubits

The basic unit of quantum information is the:

qubit

A classical bit is represented as:

0 or 1

A qubit can exist in a superposition involving:

|0⟩ and |1⟩

until measurement.

Possible physical qubit systems include:

• superconducting circuits
• trapped ions
• neutral atoms
• photons
• semiconductor spin systems

---

Quantum Computing

A quantum computer processes information using controlled quantum systems.

It uses phenomena such as:

• superposition
• entanglement
• interference
• quantum measurement

A quantum computer is not simply:

a faster ordinary computer

It represents and processes information differently.

---

Quantum Gates

Classical computers use logical operations such as:

• AND
• OR
• NOT

Quantum computers use:

quantum gates

Quantum gates manipulate the amplitudes and phases of qubit states.

Sequences of quantum gates form:

quantum circuits

The goal is to manipulate probability amplitudes so that desired answers become more likely when the system is measured.

---

Quantum Interference

Quantum algorithms depend heavily on:

interference

Probability amplitudes can interfere:

• constructively
• destructively

A successful quantum algorithm is designed so that amplitudes associated with useful results are enhanced while others are reduced.

Therefore, quantum computing is not simply "trying every answer simultaneously and reading all of them."

Measurement produces limited classical information.

The quantum algorithm must manipulate the state before measurement.

---

Potential Advantages of Quantum Computers

Quantum computers may eventually provide major advantages for certain problems.

Potential areas include:

• simulating quantum systems
• chemistry
• materials science
• optimization
• cryptography
• drug discovery
• fundamental physics

The strongest natural application is:

simulating quantum systems

because quantum computers themselves obey quantum mechanics.

---

Quantum Simulation

Simulating molecules on classical computers can become extremely difficult as the number of interacting quantum particles increases.

Quantum computers may eventually simulate:

• molecules
• chemical reactions
• catalysts
• new materials
• superconductors

more efficiently for certain problems.

This could contribute to development of:

• medicines
• batteries
• fertilizers
• industrial catalysts
• advanced materials

---

Shor's Algorithm

One famous quantum algorithm is:

Shor's algorithm

It can factor large integers much more efficiently in principle than known classical factoring methods.

This matters because some widely used public-key cryptographic systems rely on mathematical problems related to factoring or discrete logarithms.

A sufficiently capable fault-tolerant quantum computer could therefore threaten some existing cryptographic systems.

---

Post-Quantum Cryptography

The potential future threat from quantum computers has encouraged development of:

post-quantum cryptography

These are classical cryptographic algorithms designed to resist attacks from both:

• classical computers
• quantum computers

This shows that quantum technology can influence society even before large fault-tolerant quantum computers exist.

---

Grover's Algorithm

Another important quantum algorithm is:

Grover's algorithm

It provides a quadratic speedup for certain unstructured search problems.

For a search space of approximately N possibilities:

classical search may require around:

N

checks in the worst-case scale,

while Grover's algorithm requires approximately:

√N

quantum query steps.

This is an important improvement, but it is not an exponential speedup.

---

Quantum Computers Are Not Faster at Everything

A common misconception is:

quantum computers will replace ordinary computers

This is unlikely.

Classical computers are extremely effective for tasks such as:

• word processing
• web browsing
• spreadsheets
• video playback
• databases
• most everyday calculations

Quantum computers are expected to act as specialized systems for particular classes of problems.

A future computing system may combine:

classical processor + quantum processor

much like computers today can combine CPUs and specialized accelerators.

---

The Challenge of Decoherence

Quantum states are extremely sensitive to interactions with their environment.

Unwanted interactions can destroy useful quantum behaviour.

This process is called:

decoherence

Possible sources include:

• thermal energy
• electromagnetic noise
• vibration
• material imperfections
• unwanted interactions with surrounding particles

Preventing decoherence is one of the major challenges of quantum engineering.

---

Quantum Errors

Qubits are also prone to errors.

Classical computers can copy bits easily and use redundancy.

Quantum information is more difficult because unknown quantum states cannot simply be copied perfectly.

Quantum computers therefore require sophisticated:

quantum error correction

A useful error-corrected qubit may require many physical qubits.

This is one reason large-scale quantum computing is technologically difficult.

---

Extreme Cooling

Some quantum computing technologies operate at extremely low temperatures.

Superconducting quantum processors, for example, can require temperatures close to:

absolute zero

This reduces thermal disturbances and allows superconducting circuits to maintain useful quantum behaviour.

Such systems use specialized refrigerators called:

dilution refrigerators

---

Quantum Networks

Scientists are also developing:

quantum networks

These may connect distant quantum devices using photons and entanglement.

Possible future applications include:

• distributed quantum computing
• quantum communication
• highly precise synchronized measurements

A large-scale network of quantum devices is sometimes described as a possible:

quantum internet

This remains an active research area rather than a direct replacement for today's Internet.

---

Quantum Sensors and Medicine

Quantum sensors could potentially improve medical measurements.

Extremely sensitive magnetic sensors may help measure weak magnetic fields generated by:

• the brain
• the heart
• biological processes

Quantum technologies may therefore contribute to future:

diagnostic and imaging systems

---

Quantum Technology and Fundamental Science

Quantum technologies also allow scientists to test fundamental physics.

Highly precise quantum instruments can investigate:

• gravity
• relativity
• fundamental constants
• dark matter candidates
• atomic structure
• particle interactions

Technology and fundamental research reinforce each other.

Better quantum theory enables better instruments, and better instruments allow more precise tests of theory.

---

Quantum Technology and Space

Quantum technologies may also contribute to:

• satellite communication
• precision navigation
• Earth observation
• gravitational measurements
• space-based clocks

Atomic clocks are already essential to modern satellite navigation.

Future quantum sensors could provide additional capabilities.

---

Benefits to Society

Quantum technologies can provide major benefits.

Potential advantages include:

• faster solutions to certain computational problems
• improved medical technologies
• more precise sensors
• better materials
• improved scientific instruments
• secure communication techniques
• more accurate clocks and navigation
• advances in chemistry and drug research

However, technological benefits are not guaranteed simply because something is "quantum."

Each application must demonstrate a genuine advantage.

---

Economic Impact

Quantum technology is becoming an important research and industrial field.

Development requires expertise in:

• physics
• mathematics
• computer science
• electrical engineering
• materials science
• cryogenics
• photonics

This can create new industries and highly specialized careers.

It also means countries and companies may compete for:

• skilled workers
• intellectual property
• technological leadership

---

Security Implications

Quantum technology can both strengthen and challenge information security.

Potential benefit

Quantum communication can provide new methods for detecting interception.

Potential risk

Powerful quantum computers could threaten some existing cryptographic methods.

Therefore, society must prepare for both:

new opportunities and new risks

---

Ethical and Social Questions

As quantum technology develops, society may need to consider questions such as:

• Who controls powerful quantum computers?
• Who has access to expensive quantum technologies?
• How should sensitive quantum communication systems be regulated?
• How should cryptographic systems be updated?
• Could quantum advances increase technological inequality?
• How should scientific discoveries be shared?

These are not purely physics questions.

They involve:

• ethics
• economics
• law
• cybersecurity
• public policy

---

Environmental Considerations

Quantum technology can also have environmental costs and benefits.

Some systems require:

• complex manufacturing
• specialized materials
• significant cooling equipment
• substantial infrastructure

However, quantum technologies may eventually contribute to:

• better battery materials
• improved catalysts
• more efficient industrial processes
• improved energy technologies

The total environmental impact depends on how technologies are developed and used.

---

Evaluating Quantum Technology

A balanced evaluation should consider both advantages and limitations.

Potential benefits

• powerful new scientific tools
• improved sensors
• advanced communication
• new computational capabilities
• better materials and medicines
• increased understanding of nature

Challenges

• high cost
• technical complexity
• decoherence
• quantum errors
• specialized infrastructure
• cybersecurity risks
• uncertain timelines for some applications
• possible unequal access

Quantum technology has enormous potential, but expectations should be based on evidence rather than hype.

---

Established vs Emerging Technologies

It is useful to distinguish technologies that already have widespread impact from those still being developed.

Quantum physics is therefore not merely a future technology.

It already underlies much of modern civilization.

---

Worked Example: Laser Photon

Suppose a laser transition has:

ΔE = 3.0 × 10⁻¹⁹ J

Using:

ΔE = hf

f = ΔE/h

f = (3.0 × 10⁻¹⁹)/(6.63 × 10⁻³⁴)

f ≈ 4.52 × 10¹⁴ Hz

The emitted photons therefore have frequency approximately:

4.5 × 10¹⁴ Hz

---

Worked Example: Photon Wavelength

Using:

c = fλ

for:

f = 4.52 × 10¹⁴ Hz

λ = c/f

λ = (3.00 × 10⁸)/(4.52 × 10¹⁴)

λ ≈ 6.64 × 10⁻⁷ m

or:

664 nm

This corresponds approximately to red visible light.

The colour of the laser is therefore connected directly to:

quantized energy transitions

---

Worked Example: Semiconductor Photon

Suppose an electron loses:

2.0 eV

of energy during a transition.

The emitted photon also carries approximately:

2.0 eV

Using:

E = hf

the photon frequency can be determined.

Thus the quantum energy structure of the semiconductor controls the emitted light.

This principle is used in:

LED design

---

Worked Example: Classical Bit vs Qubit

A classical bit might contain:

0

or:

1

A qubit might be prepared as:

|ψ⟩ = α|0⟩ + β|1⟩

If:

|α|² = 0.75

and:

|β|² = 0.25

then measurement gives:

0 with probability 75%

and:

1 with probability 25%

The qubit is not simply an unknown classical bit. Before measurement, the quantum state includes probability amplitudes that can interfere during quantum operations.

---

From Quantum Theory to Modern Society

The development of quantum technology can be summarized as:

quantum theory

↓

understanding atoms, electrons and photons

↓

lasers and semiconductors

↓

transistors and integrated circuits

↓

computers, communication and digital technology

and increasingly:

superposition + entanglement + precise quantum control

↓

quantum computers + sensors + communication

Quantum physics therefore connects some of the most abstract ideas in science with some of the most important technologies in society.

---

Common Mistakes

Mistake: Saying quantum technology means only quantum computers.
Lasers, transistors, LEDs, solar cells and atomic clocks already depend on quantum physics.

Mistake: Saying lasers produce ordinary random light.
Stimulated emission produces highly coherent and directional light.

Mistake: Saying stimulated emission produces a photon with unrelated properties.
The stimulated photon matches important properties of the stimulating photon.

Mistake: Saying semiconductors are simply poor conductors.
Their energy-band structures allow conductivity to be precisely controlled.

Mistake: Saying a qubit is simply both 0 and 1 in the classical sense.
A qubit exists in a quantum state involving probability amplitudes and phase.

Mistake: Saying quantum computers calculate every possible answer and then reveal all of them.
Quantum algorithms use interference to manipulate amplitudes before measurement.

Mistake: Saying quantum computers will make every calculation faster.
Their advantages apply to particular types of problems.

Mistake: Saying quantum communication automatically makes an entire computer system impossible to hack.
Quantum protocols can provide specific security advantages, but real systems still have hardware, software and implementation vulnerabilities.

Mistake: Saying entanglement allows messages to travel faster than light.
Entanglement does not permit controllable faster-than-light communication.

Mistake: Treating all predicted quantum technologies as already mature.
Some quantum technologies are established, while others remain active areas of research and development.

---

Key Terms

Quantum technology — technology that uses principles or effects described by quantum physics.

Quantization — restriction of certain physical quantities to discrete allowed values.

Photon — quantum of electromagnetic radiation.

Stimulated emission — process in which an incoming photon causes an excited system to emit a matching photon.

Population inversion — condition in which more particles occupy a relevant excited state than a lower-energy state.

Laser — device that uses stimulated emission to produce highly controlled electromagnetic radiation.

Coherent light — light whose waves maintain well-defined phase relationships.

Semiconductor — material whose electronic properties can be controlled between conducting and insulating behaviour.

Energy band — range of allowed electron energies in a solid.

Band gap — energy range separating important allowed energy bands.

Doping — addition of impurities to modify semiconductor electrical properties.

Transistor — semiconductor device used for switching or amplification.

Qubit — fundamental unit of quantum information.

Superposition — quantum state involving a combination of possible basis states.

Entanglement — quantum correlation between systems that cannot generally be described independently.

Quantum interference — combination of quantum probability amplitudes that can enhance or suppress possible outcomes.

Decoherence — loss of useful quantum behaviour through interaction with the environment.

Quantum error correction — techniques used to protect quantum information from errors.

Quantum computing — computation using controlled quantum states and operations.

Quantum communication — use of quantum states to transmit or protect information.

Quantum key distribution (QKD) — method for establishing cryptographic key material using quantum states.

Quantum sensor — device exploiting quantum effects to make highly precise measurements.

Atomic clock — clock using stable quantum transitions in atoms as a frequency reference.

Scanning tunneling microscope (STM) — instrument that uses electron tunneling to investigate surfaces at extremely small scales.

---

Key Takeaways

• Quantum technology applies the principles of quantum physics to practical devices.
• Modern society already relies heavily on quantum technologies.
• Lasers depend on quantized energy levels and stimulated emission.
• Laser photon energy satisfies ΔE = hf.
• Population inversion is required for sustained laser amplification.
• Semiconductors are understood using quantum energy bands.
• The band gap helps determine the electrical and optical behaviour of a semiconductor.
• Doping creates useful n-type and p-type semiconductor materials.
• Semiconductor technology enables transistors, LEDs, solar cells and computer chips.
• Quantum tunneling is used in devices such as scanning tunneling microscopes and tunnel diodes.
• Atomic clocks use highly stable quantum transitions to measure time extremely precisely.
• Emerging quantum technologies include quantum computing, communication, sensing, simulation and networking.
• A quantum bit is called a qubit.
• Qubits can exist in superpositions of basis states.
• Entanglement creates uniquely quantum correlations between systems.
• Quantum algorithms use interference to manipulate probability amplitudes.
• Quantum computers are not simply faster versions of classical computers.
• Quantum computers may provide major advantages for certain specialized problems.
• Quantum simulation could contribute to chemistry, medicine and materials science.
• Large-scale quantum computing faces major challenges including decoherence and errors.
• Quantum error correction will be important for fault-tolerant quantum computing.
• Quantum communication can provide new methods of detecting interception.
• Powerful future quantum computers could threaten some existing cryptographic systems.
• Post-quantum cryptography is being developed to address this risk.
• Quantum sensors may enable extremely precise measurements in science, medicine and navigation.
• Quantum technology offers major opportunities but also raises economic, security, ethical and environmental questions.
• Quantum physics has progressed from an abstract scientific theory into one of the foundations of modern technological society.

Check Your Understanding

1. What is quantum technology?
2. Give four examples of established technologies that depend on quantum physics.
3. Explain how quantized energy levels are involved in laser operation.
4. What is stimulated emission?
5. Why is population inversion important in a laser?
6. Give three practical applications of lasers.
7. What is a semiconductor?
8. Explain the difference between the valence band, conduction band and band gap.
9. What is semiconductor doping?
10. Explain why transistors are important to modern computing.
11. How does an LED demonstrate the quantum nature of energy?
12. Describe one technological application of quantum tunneling.
13. How do atomic clocks use quantum physics?
14. What is a qubit?
15. Explain the meaning of quantum superposition.
16. What is quantum entanglement, and why is it useful?
17. Explain why a quantum computer is not simply a faster classical computer.
18. Describe two potential applications and two major challenges of quantum computing.
19. Explain one way quantum technology could improve society and one way it could create a new risk.
20. Evaluate the statement: "Quantum physics is only important for theoretical science and has little effect on everyday life."