![\"\"](\"https:\/\/cdn.arstechnica.net\/wp-content\/uploads\/2021\/01\/quantum-series-1-800x450.jpg\" "\\"\\"")
Exploring the quantum world<\/h2>\n\n\n\n- A curious observer\u2019s guide to quantum mechanics, pt. 3: Rose colored glasses <\/a><\/li>
- A curious observer\u2019s guide to quantum mechanics, pt. 2: The particle melting pot<\/a><\/li>
- A \u201cno math\u201d (but seven-part) guide to modern quantum mechanics<\/a><\/li><\/ul>\n\n\n\n
View more stories<\/a><\/p>\n\n\n\nSome technical revolutions enter with drama and a bang, others wriggle unnoticed into our everyday experience. And one of the quietest revolutions of our current century has been the entry of quantum mechanics into our everyday technology. It used to be that quantum effects were confined to physics laboratories and delicate experiments. But modern technology increasingly relies on quantum mechanics for its basic operation, and the importance of quantum effects will only grow in the decades to come.<\/p>\n\n\n\n
As such, the time has come to explain quantum mechanics\u2014or, at least, its basics.<\/p>\n\n\n\n
My goal in this seven(!)-part series is to introduce the strangely beautiful effects of quantum mechanics and explain how they\u2019ve come to influence our everyday world. Each edition will include a guided hike into the quantum mechanical woods where we\u2019ll admire a new\u2014and often surprising\u2014effect. Once back at the visitor\u2019s center, we\u2019ll talk about how that effect is used in technology and where to look for it.<\/p>\n\n\n\n
Embarking on a series of quantum mechanics articles can be intimidating. Few things trigger more fear than \u201ca simple introduction to physics.\u201d But to the intrepid and brave, I will make a few promises before we start:<\/p>\n\n\n\n
- No math. While the language of quantum mechanics is written using fairly advanced math, I don\u2019t believe one has to read Japanese before you can appreciate Japanese art. Our journey will focus on the beauty of the quantum world.<\/li>
- No philosophy. There has been a fascination with the \u2018meaning\u2019 of quantum mechanics, but we\u2019ll leave that discussion for pints down at the pub. Here we will focus on what we see.<\/li>
- Everything we encounter will be experimentally verified. While some of the results might be surprising, nothing we encounter will be speculative.<\/li><\/ul>\n\n\n\n
If you choose to follow me through this series of articles, we will see quantum phenomena on galactic scales, watch particles blend and mix, and see how these effects give rise to both our current technology and advances that are on the verge of making it out of the lab.<\/p>\n\n\n\n
So put on your mental hiking boots, grab your binoculars, and follow me as we set out to explore the quantum world.<\/p>\n\n\n\n
What is quantum mechanics?<\/h2>\n\n\n\n
My Mom once asked me, \u201cWhat is quantum mechanics?\u201d This question has had me stumped for a while now. My best answer so far is that quantum mechanics is the study of how small particles move and interact. But that\u2019s an incomplete answer, since quantum effects can be important on galactic scales too. And it is doubly unsatisfactory because many effects like superconductivity are caused by the blending and mixing of multiple particles.Advertisementhttps:\/\/946fac658dd4b954a829965fa9e63e19.safeframe.googlesyndication.com\/safeframe\/1-0-37\/html\/container.html<\/p>\n\n\n\n
In many ways, the role of quantum mechanics can be understood in analogy with Newtonian gravity and Einstein\u2019s general relativity. Both describe gravity, but general relativity is more correct\u2014it describes how the Universe works in every situation we\u2019ve managed to test. But 99.99 percent of the time, Newtonian gravity and general relativity give the same answer, and Newtonian gravity is much<\/em> easier to use. So unless we\u2019re near a black hole, or making precision measurements of time with an optical clock, Newtonian gravity is good enough.<\/p>\n\n\n\nSimilarly classical mechanics and quantum mechanics both describe motions and interactions. Quantum mechanics is more right, but most of the time classical mechanics is good enough.<\/p>\n\n\n\n
What I find fascinating is that “good enough” increasingly isn\u2019t. Much of the technology developed in this century is starting to rely on quantum mechanics\u2014classical mechanics is no longer accurate enough to understand how these inventions work.<\/p>\n\n\n\n
So let\u2019s start today\u2019s hike with a deceptively simple question, \u201cHow do particles move?\u201d<\/p>\n\n\n\n
Kitchen quantum mechanics<\/h2>\n\n\n\n
Some of the experiments we will see require specialized equipment, but let\u2019s start with an experiment you can do at home. Like a cooking show, I\u2019ll explain how to do it, but you are encouraged to follow along and do the experiment for yourself. (Share your photos in the discussion below. Bonus points for setting the experiment up in your cubicle\/place of work\/other creative setting.)<\/p>\n\n\n\n
To study how particles move, we need a good particle pea shooter to make lots of particles for us to play with. It turns out a laser pointer, in addition to entertaining the cat, is a great<\/em> source of particles. It makes copious amounts of photons, all moving in nearly the same direction and with nearly the same energy (as indicated by their color).<\/p>\n\n\n\nIf we look at the light from a laser pointer, it exits the end of the laser pointer and moves in a straight line until it hits an obstacle and scatters (or hits a mirror and bounces). At this point, it is tempting to guess that we know how particles move: they exit the end of the laser like little ball bearings and move in a straight line until they hit something. But as good observers, let\u2019s make sure.<\/p>\n\n\n\n
Let\u2019s challenge the particles with an obstacle course by cutting thin slits in aluminum foil with razor blades. In the aluminum foil I\u2019ve made a couple of different cuts. The first is a single slit, a few millimeters long. For the second I\u2019ve stacked two razor blades together and used them to cut two parallel slits a few tenths of a millimeter apart.Advertisementhttps:\/\/946fac658dd4b954a829965fa9e63e19.safeframe.googlesyndication.com\/safeframe\/1-0-37\/html\/container.html<\/p>\n\n\n\n![\"Horizontal](\"https:\/\/cdn.arstechnica.net\/wp-content\/uploads\/2020\/03\/Aluminum-foil-slits-2-640x762.jpg\" "\\"\\"")
<\/a>Enlarge<\/a> \/ Horizontal slits in aluminum foil made with razor blades. The upper slit is from a single blade, while the lower is from two blades taped together.Miguel Morales<\/figcaption><\/figure>\n\n\n\nIn a darkened room, I setup my laser pointer to shoot across the room and hit a blank wall. As expected I see a spot (provided the cat\u2019s not around). Next, I put the single slit in the aluminum foil in the laser\u2019s path and look at the pattern on the wall. When we send the light through the single slit, we see that the beam dramatically expands in the direction perpendicular<\/em> to the slit\u2014not along the slit.<\/p>\n\n\n\n![\"Laser](\"https:\/\/cdn.arstechnica.net\/wp-content\/uploads\/2020\/03\/Single-slit-640x999.jpeg\" "\\"\\"")
<\/a>Enlarge<\/a> \/ Laser light passing through the single horizontal slit is spread verticallyMiguel Morales<\/figcaption><\/figure>\n\n\n\nInteresting. But let\u2019s press on.<\/p>\n\n\n\n
Now let\u2019s put the closely spaced slits into the laser beam. The light is again spread out, but now there is a stripey pattern.<\/p>\n\n\n\n![\"Laser](\"https:\/\/cdn.arstechnica.net\/wp-content\/uploads\/2020\/03\/Double-slit-640x961.jpeg\" "\\"\\"")
<\/a>Enlarge<\/a> \/ Laser light passing through the two horizontal slits produces the distinctive stripes of quantum mechanics.Miguel Morales<\/figcaption><\/figure>\n\n\n\nCongratulations! You\u2019ve just spotted a quantum mechanical effect! (whoo hoo animated emoji) This is the classic double-slit experiment. The stripey pattern is called interference, and is a telltale signature of quantum mechanics. We will see a lot of stripes like these.<\/p>\n\n\n\n
Now you have probably seen interference like this before, since water and sound waves show exactly this kind of striping.<\/p>\n\n\n\n![\"Water](\"https:\/\/cdn.arstechnica.net\/wp-content\/uploads\/2020\/03\/Water-interference-640x360.jpg\" "\\"\\"")
<\/a>Enlarge<\/a> \/ Water waves from two sources (one visible in green, the other hidden behind the presenter). The circular waves overlap into regions of extra strength (bright stripes) and regions where the waves cancel each other out (dark bands). The formation of stripes is a signature of wave motion.Veritasium<\/a><\/figcaption><\/figure>\n\n\n\nIn the photo above, each ball creates waves that move out in a circle. But a wave has both a peak and a trough. In some places the peak of the wave from one of the balls always coincides with the trough from the other (and vice versa). In these areas the waves always cancel out and the water is calm. In other locations the peaks of the waves from both balls always arrive together and add up to make a wave that is extra tall. In these locations the troughs also add up to be extra deep.<\/p>\n\n\n\n
So does the fact that we are seeing stripes when our laser pointer goes through two slits mean that particles are waves? To answer that question, we\u2019re going to have to look more closely.<\/p>\n\n\n\n
ARS VIDEO<\/h3>\n\n\n\n
Quantum mechanics fractals – “chaotic systems” | Ars Technica<\/a>https:\/\/946fac658dd4b954a829965fa9e63e19.safeframe.googlesyndication.com\/safeframe\/1-0-37\/html\/container.htmlhttps:\/\/946fac658dd4b954a829965fa9e63e19.safeframe.googlesyndication.com\/safeframe\/1-0-37\/html\/container.html<\/p>\n\n\n\nThe professional kitchen<\/h2>\n\n\n\n
The double slits served two purposes: each slit spread the beam out (as we saw when we went through just one slit), while the two closely spaced slits provided the particles with a choice as to which slit to pass through. We can use a different experimental setup to more clearly separate the act of spreading the beam and forcing a choice, and this bigger setup will allow us to study in detail what is happening. (This is the moment in the cooking show where they pull out some obscure cooking tool\u2014like a cr\u00e8me br\u00fbl\u00e9e torch\u2014that you\u2019re unlikely to have at home.)<\/p>\n\n\n\n![\"The](\"https:\/\/cdn.arstechnica.net\/wp-content\/uploads\/2020\/03\/Bigger-setup-diagram-v2-640x493.jpg\" "\\"\\"")
<\/a>Enlarge<\/a> \/ The professional version of the two slits in aluminum foil. Here the light beam is split by a half silvered mirror and sent into left and right paths. These paths are then recombined to show stripes.Miguel Morales<\/figcaption><\/figure>\n\n\n\nKeeping the laser, let\u2019s use a lens to spread the beam out, and then a half-silvered mirror to give the particles a one-way-or-the-other choice. We then use a couple of good mirrors and another half-silvered mirror to recombine the beams before they reach a wall or screen, as shown above. If one of the mirrors is mis-aligned ever so slightly, we will again see stripes (places where waves add together and cancel out). In the 38 second video below I show the working version.https:\/\/player.vimeo.com\/video\/396805337?color=ff9933<\/p>\n\n\n\n
What I find fun about this setup is that it is big<\/em>. I don\u2019t need a microscope to mess with it. For convenience, I made this table top sized, but we could have made it huge. In the LIGO experiment used to detect gravitational waves, the light is sent down arms 4 km long, and with radio light we\u2019ve used the Cassini spacecraft as it approached Saturn as a mirror. Quantum mechanics is not limited to the microscopic world.<\/p>\n\n\n\nBut let\u2019s play with our human sized experiment, and see some more quantum mechanical effects.<\/p>\n\n\n\n
Slow mo<\/h2>\n\n\n\n
The first thing I’d like to do is to look very carefully at the stripey pattern. Instead of just looking at the screen, let\u2019s use a sensitive camera so we can watch it as it develops. When the laser is bright, the camera will immediately capture stripes. But if we make the room very<\/em> dark and turn down the strength of the laser, we will notice that light is a not smoothly distributed, but appears at individual \u2018points\u2019\u2014in slow motion we can see the arrival of individual photons. They look like small red paintballs hitting the camera sensor.Advertisementhttps:\/\/946fac658dd4b954a829965fa9e63e19.safeframe.googlesyndication.com\/safeframe\/1-0-37\/html\/container.html
View more stories<\/a><\/p>\n\n\n\n Some technical revolutions enter with drama and a bang, others wriggle unnoticed into our everyday experience. And one of the quietest revolutions of our current century has been the entry of quantum mechanics into our everyday technology. It used to be that quantum effects were confined to physics laboratories and delicate experiments. But modern technology increasingly relies on quantum mechanics for its basic operation, and the importance of quantum effects will only grow in the decades to come.<\/p>\n\n\n\n As such, the time has come to explain quantum mechanics\u2014or, at least, its basics.<\/p>\n\n\n\n My goal in this seven(!)-part series is to introduce the strangely beautiful effects of quantum mechanics and explain how they\u2019ve come to influence our everyday world. Each edition will include a guided hike into the quantum mechanical woods where we\u2019ll admire a new\u2014and often surprising\u2014effect. Once back at the visitor\u2019s center, we\u2019ll talk about how that effect is used in technology and where to look for it.<\/p>\n\n\n\n Embarking on a series of quantum mechanics articles can be intimidating. Few things trigger more fear than \u201ca simple introduction to physics.\u201d But to the intrepid and brave, I will make a few promises before we start:<\/p>\n\n\n\n If you choose to follow me through this series of articles, we will see quantum phenomena on galactic scales, watch particles blend and mix, and see how these effects give rise to both our current technology and advances that are on the verge of making it out of the lab.<\/p>\n\n\n\n So put on your mental hiking boots, grab your binoculars, and follow me as we set out to explore the quantum world.<\/p>\n\n\n\n My Mom once asked me, \u201cWhat is quantum mechanics?\u201d This question has had me stumped for a while now. My best answer so far is that quantum mechanics is the study of how small particles move and interact. But that\u2019s an incomplete answer, since quantum effects can be important on galactic scales too. And it is doubly unsatisfactory because many effects like superconductivity are caused by the blending and mixing of multiple particles.Advertisementhttps:\/\/946fac658dd4b954a829965fa9e63e19.safeframe.googlesyndication.com\/safeframe\/1-0-37\/html\/container.html<\/p>\n\n\n\n In many ways, the role of quantum mechanics can be understood in analogy with Newtonian gravity and Einstein\u2019s general relativity. Both describe gravity, but general relativity is more correct\u2014it describes how the Universe works in every situation we\u2019ve managed to test. But 99.99 percent of the time, Newtonian gravity and general relativity give the same answer, and Newtonian gravity is much<\/em> easier to use. So unless we\u2019re near a black hole, or making precision measurements of time with an optical clock, Newtonian gravity is good enough.<\/p>\n\n\n\n Similarly classical mechanics and quantum mechanics both describe motions and interactions. Quantum mechanics is more right, but most of the time classical mechanics is good enough.<\/p>\n\n\n\n What I find fascinating is that “good enough” increasingly isn\u2019t. Much of the technology developed in this century is starting to rely on quantum mechanics\u2014classical mechanics is no longer accurate enough to understand how these inventions work.<\/p>\n\n\n\n So let\u2019s start today\u2019s hike with a deceptively simple question, \u201cHow do particles move?\u201d<\/p>\n\n\n\n Some of the experiments we will see require specialized equipment, but let\u2019s start with an experiment you can do at home. Like a cooking show, I\u2019ll explain how to do it, but you are encouraged to follow along and do the experiment for yourself. (Share your photos in the discussion below. Bonus points for setting the experiment up in your cubicle\/place of work\/other creative setting.)<\/p>\n\n\n\n To study how particles move, we need a good particle pea shooter to make lots of particles for us to play with. It turns out a laser pointer, in addition to entertaining the cat, is a great<\/em> source of particles. It makes copious amounts of photons, all moving in nearly the same direction and with nearly the same energy (as indicated by their color).<\/p>\n\n\n\n If we look at the light from a laser pointer, it exits the end of the laser pointer and moves in a straight line until it hits an obstacle and scatters (or hits a mirror and bounces). At this point, it is tempting to guess that we know how particles move: they exit the end of the laser like little ball bearings and move in a straight line until they hit something. But as good observers, let\u2019s make sure.<\/p>\n\n\n\n Let\u2019s challenge the particles with an obstacle course by cutting thin slits in aluminum foil with razor blades. In the aluminum foil I\u2019ve made a couple of different cuts. The first is a single slit, a few millimeters long. For the second I\u2019ve stacked two razor blades together and used them to cut two parallel slits a few tenths of a millimeter apart.Advertisementhttps:\/\/946fac658dd4b954a829965fa9e63e19.safeframe.googlesyndication.com\/safeframe\/1-0-37\/html\/container.html<\/p>\n\n\n\n In a darkened room, I setup my laser pointer to shoot across the room and hit a blank wall. As expected I see a spot (provided the cat\u2019s not around). Next, I put the single slit in the aluminum foil in the laser\u2019s path and look at the pattern on the wall. When we send the light through the single slit, we see that the beam dramatically expands in the direction perpendicular<\/em> to the slit\u2014not along the slit.<\/p>\n\n\n\n Interesting. But let\u2019s press on.<\/p>\n\n\n\n Now let\u2019s put the closely spaced slits into the laser beam. The light is again spread out, but now there is a stripey pattern.<\/p>\n\n\n\n Congratulations! You\u2019ve just spotted a quantum mechanical effect! (whoo hoo animated emoji) This is the classic double-slit experiment. The stripey pattern is called interference, and is a telltale signature of quantum mechanics. We will see a lot of stripes like these.<\/p>\n\n\n\n Now you have probably seen interference like this before, since water and sound waves show exactly this kind of striping.<\/p>\n\n\n\n In the photo above, each ball creates waves that move out in a circle. But a wave has both a peak and a trough. In some places the peak of the wave from one of the balls always coincides with the trough from the other (and vice versa). In these areas the waves always cancel out and the water is calm. In other locations the peaks of the waves from both balls always arrive together and add up to make a wave that is extra tall. In these locations the troughs also add up to be extra deep.<\/p>\n\n\n\n So does the fact that we are seeing stripes when our laser pointer goes through two slits mean that particles are waves? To answer that question, we\u2019re going to have to look more closely.<\/p>\n\n\n\n Quantum mechanics fractals – “chaotic systems” | Ars Technica<\/a>https:\/\/946fac658dd4b954a829965fa9e63e19.safeframe.googlesyndication.com\/safeframe\/1-0-37\/html\/container.htmlhttps:\/\/946fac658dd4b954a829965fa9e63e19.safeframe.googlesyndication.com\/safeframe\/1-0-37\/html\/container.html<\/p>\n\n\n\n The double slits served two purposes: each slit spread the beam out (as we saw when we went through just one slit), while the two closely spaced slits provided the particles with a choice as to which slit to pass through. We can use a different experimental setup to more clearly separate the act of spreading the beam and forcing a choice, and this bigger setup will allow us to study in detail what is happening. (This is the moment in the cooking show where they pull out some obscure cooking tool\u2014like a cr\u00e8me br\u00fbl\u00e9e torch\u2014that you\u2019re unlikely to have at home.)<\/p>\n\n\n\n Keeping the laser, let\u2019s use a lens to spread the beam out, and then a half-silvered mirror to give the particles a one-way-or-the-other choice. We then use a couple of good mirrors and another half-silvered mirror to recombine the beams before they reach a wall or screen, as shown above. If one of the mirrors is mis-aligned ever so slightly, we will again see stripes (places where waves add together and cancel out). In the 38 second video below I show the working version.https:\/\/player.vimeo.com\/video\/396805337?color=ff9933<\/p>\n\n\n\n What I find fun about this setup is that it is big<\/em>. I don\u2019t need a microscope to mess with it. For convenience, I made this table top sized, but we could have made it huge. In the LIGO experiment used to detect gravitational waves, the light is sent down arms 4 km long, and with radio light we\u2019ve used the Cassini spacecraft as it approached Saturn as a mirror. Quantum mechanics is not limited to the microscopic world.<\/p>\n\n\n\n But let\u2019s play with our human sized experiment, and see some more quantum mechanical effects.<\/p>\n\n\n\n The first thing I’d like to do is to look very carefully at the stripey pattern. Instead of just looking at the screen, let\u2019s use a sensitive camera so we can watch it as it develops. When the laser is bright, the camera will immediately capture stripes. But if we make the room very<\/em> dark and turn down the strength of the laser, we will notice that light is a not smoothly distributed, but appears at individual \u2018points\u2019\u2014in slow motion we can see the arrival of individual photons. They look like small red paintballs hitting the camera sensor.Advertisementhttps:\/\/946fac658dd4b954a829965fa9e63e19.safeframe.googlesyndication.com\/safeframe\/1-0-37\/html\/container.htmlWhat is quantum mechanics?<\/h2>\n\n\n\n
Kitchen quantum mechanics<\/h2>\n\n\n\n
<\/a><\/a><\/a><\/a>ARS VIDEO<\/h3>\n\n\n\n
The professional kitchen<\/h2>\n\n\n\n
<\/a>Slow mo<\/h2>\n\n\n\n