Section 3.6: Applications of Quantum Mechanics
Section 3.6 Questions, page 176
1. Lasers work on a principle of raising many electrons to a higher energy level through
absorption of energy, and then stimulating them to drop to a lower level all at once, producing an
emission of a very large number of photons. The emission spectra will contain the colour of light
the laser will produce.
2. If the mirrors in a laser were misaligned, the intensity of the laser beam would likely be low
because it would not be able to build up a large number of photons.
3. Answers may vary. Students’ posters should include descriptions of four everyday objects,
e.g., video game consoles use lasers to read the information on game disks, a laser is used to
detect if you cross onto the lane while you bowl, bar code scanners use lasers, and lasers are used
to make light shows at music concerts.
4. Bose–Einstein condensates were only theoretical until the mid-1990s because until then the
technology did not exist to bring the temperature close to 0 K, the temperature at which the
condensates occur.
5.
6. The primary advantage of MRI over X-rays and CT scans is that it does not use ionizing
radiation to form an image, resulting in less damage to DNA and other macromolecules.
7. (a) Answers may vary. Sample answer: Quantum computing is the use of the quantum
mechanical properties of atomic scale processes to code for quantum bits (qubits) of information.
Classic computing has reached a limit because at very small scales the processors are under the
control of quantum mechanics.
(b) Answers may vary. Sample answer: Modern computing information is discrete and codes
using 1 and 0 on physical circuits. Quantum computing uses atoms and molecules to code for
quantum information. These bits have unique properties like “superpositioning”, being 0 and 1
simultaneously, and “entanglement”.
(c) Answers may vary. Sample answer: Quantum computing is better than traditional computing
because it can utilize different algorithms that that can model complex problems.
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Chapter 3: Atoms 3.6-1
(d) Answers may vary. Sample answer: One drawback to quantum computing is that we do not
currently have the algorithms to perform quantum computing in real polynomial time.
8. (a) Answers may vary. Answers may include information such as the following: RSA is an
algorithm that is used as a cryptographic tool to generate keys that decipher an encrypted
message. It is commonly used for many security applications. The system needs increasingly
larger key sizes as algorithms have been developed that can break the previously sufficientlysized keys.
(b) Answers may vary. Sample answer: Quantum cryptography has been used to produce
quantum keys that cannot be observed by outside parties because of quantum interference.
(c) Photons are used in quantum cryptography as a medium on which the message is sent.
Polarization is used in quantum cryptography to transform the transmitted photons into a binary
code, which can be interpreted.
(d) Answers may vary. Sample answer: To send a quantum-encrypted message, a sender codes a
message in 1s and 0s and sends the receiver the code as a sequence of photons that have been
polarized vertically or at a 45° angle. The receiver has a set of filters that either detect or block
the incoming photons. The photons that are detected are converted into 1s and 0s and used as a
key. Since an outside observer does not know what filters the sender and receiver are using, the
key is secure.
(e) Answers may vary. Sample answer: One advantage quantum cryptography has over
traditional cryptography is that outside observers cannot obtain the key by observing the message
in quantum cryptography.
9. A gas laser uses gas phase molecules that are excited by a power source to produce a photon
emission. Gas phase lasers are used to do research. A chemical laser uses a chemical reaction to
excite molecules that produces a photon emission. For this reason chemical lasers require
constant recharging and are very large, and they are often used in industrial and military settings.
10. Answers may vary. Answers may include information such as: Depression is a neurological
disorder that results in negative emotional states. MRI has been used to determine which
cognitive areas are associated with depressive states. Also, Dr. Jianfeng Feng of the University
of Warwick has found that many depressed patients have a decoupling of “hate circuits”
following scanning in a MRI machine. These results suggest that magnetic fields could also be
used to alter the neuro-circuitry of depressed individuals.
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Chapter 3: Atoms 3.6-2